UNC 

HEALTH  SCIENCES  LIBRARY 


The  Sheldon  Peck  Collection 
on  the  History  of  Orthodontics 
and  Dental  Medicine 

Gift  of 

Sheldon  Peck,  DDS  1966 

and 

Leena  Peck,  DMD 


A  MANUAL 

OF 

DENTAL  ANATOMY 

£B.&..WALT£B 


. 


It,/? 


A  MANUAL 


OF 


DENTAL  ANATOMY 


HUMAN  AND  COMPARATIVE 


BY 

CHARLES  S.  TOMES,  M.A.,  F.R.S. 


WITH  212  ILLUSTRATIONS 


THIRD  EDITION 


PHILADELPHIA 

P.  BLAKISTON,  SON  &  CO. 

1012  WALNUT  STREET 

1890 


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1 


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PREFACE  TO  THE  THIRD  EDITION. 


In  the  following  pages  it  has  been  my  endeavour  to 
give  an  outline  of  the  more  important  facts  of  Odon¬ 
tology,  such  as  may  serve  for  an  introduction  to  a 
more  extended  study  of  the  subject.  Within  the 
limitations  of  an  elementary  text-book,  more  than  this 
seems  not  to  be  practicable,  and  I  have  therefore 
omitted,  or  passed  by  with  brief  mention,  hypotheses 
as  to  the  genesis  of  teeth  and  the  like,  which,  however 
interesting,  have  not  as  yet  so  established  themselves 
as  to  meet  with  general  acceptance. 

In  a  book  of  this  kind  it  is  neither  desirable  to 
burden  the  text  with  many  references,  nor  to  omit 
them  altogether  ;  the  rule  which  I  have  followed,  I 
fear  by  no  means  always  consistently,  has  been  to  give 
references  only  to  works  and  papers  which  might  be 
regarded  as  in  a  measure  classical,  and  to  those  which, 
by  reason  of  being  somewhat  new,  have  not  yet  found 
their  way  into  systematic  treatises. 


VI 


FREFA  CE. 


But  I  must  take  this  opportunity  of  expressing  my 
obligation  to  the  Odontographies  of  Prof.  Owen  and 
of  Giebel,  to  Prof.  Flower’s  Lectures  on  Odontology, 
his  articles  in  the  Encyclopaedia  Britannica,  and 
his  many  other  papers ;  to  the  article  on  Teeth  by 
Dr.  Worthman  in  the  “  American  System  of  Dental 
Surgery,”  and  to  the  rich  contributions  of  Prof.  Cope 
and  Prof.  Marsh  to  our  knowledge  of  the  varied 
extinct  mammalian  fauna  ot  America,  of  all  of  which 
I  have  made  free  use. 

CHARLES  S.  TOMES. 

37,  Cavendish  Square, 

Nov.  1889. 


TABLE  OF  CONTENTS 


—  v  __ 

CHAPTER  I. 

PAGE 

The  Nature  of  Teeth  -Description  of  the  Teeth  of  Man  .  1 

CHAPTER  II. 

The  Maxillary  Bones,  and  Associated  Parts  .  .  ,  25 


The  Dental  Tissues  : 
Pulp,  &c. 

CHAPTER  III. 

Enamel,  Dentine,  Cementum,  Tooth 

. . 43 

CHAPTER  IV. 

The  Development  of  the  Teeth — in  Fish — in  Reptiles — in 

Mammals— Calcification  of  the  Dental  Tissues  .  .  .  121 

CHAPTER  Y. 

The  Development  of  the  Jaws  and  the  Eruption  and  Attach¬ 
ment  of  the  Teeth  ........  186 

CHAPTER  VI. 


The  Teeth  of  Fishes 


.  227 


Vlll 


CONTENTS. 


CHAPTER  VII. 

PAGE 

The  Teeth  oe  Batrachia,  Reptiles,  and  Birds  .  .  .  256 


CHAPTER  VIII. 

The  Teeth  oe  Mammals— Introductory  Remarks  —  Homologies 

op  the  Teeth — Milk  Dentition  .  .  ...  .  283 


CHAPTER  IX. 

The  Teeth  oe  Edentata,  Cetacea,  and  Sirenia  .  .  .  333 


CHAPTER  X. 

The  Teeth  oe  Insectiyora,  Chiroptera,  Rodentia,  Hyracoidea, 

Proboscidea,  Ungulata,  Carnivora,  Primates  .  .  .  349 


CHAPTER  XI. 

The  Teeth  oe  Marsupialia 


.  464 


A 

MANUAL  OF  DENTAL  ANATOMY 

HUMAN  AND  COMPARATIVE. 


CHAPTER  I. 

•  % 

THE  TEETH  OF  MAN. 

The  range  of  the  subject  of  Dental  Anatomy  turns  upon 
the  meaning  which  is  attached  to  the  word  “  Tooth  ;  ”  but, 
although  this  chapter  might  most  appropriately  open  with 
a  definition  of  this  word,  it  is  very  much  easier  to  explain 
what  is  ordinarily  understood  by  it,  than  to  frame  any 
single  sentence  which  shall  fulfil  the  requirements  of  logical 
definition.  Most  vertebrate  and  a  great  many  invertebrate 
animals  have  certain  hard  masses  in  or  near  to  the  orifice 
of  the  alimentary  canal,  i.e.,  the  mouth;  by  these  hard 
masses,  sometimes  of  bony  and  sometimes  of  horny  nature, 
various  offices  in  connection  with  the  prehension  or  com¬ 
minution  of  food  are  performed,  and  to  them  the  term 
“  teeth  ”  is  applied.  But  whilst  in  some  animals  these 
functions  are  performed  by  horny  bodies,  recent  researches 
have  shown  that,  at  all  events  in  several  cases,  these  horny 
teeth  are  superimposed  upon  true  tooth  germs,  calcified  to 
some  extent,  which  they  supersede ;  the  exact  relation 
of  the  one  to  the  other  requires  further  elucidation.  In 


B 


2 


A  MANUAL  OF  DENTAL  ANATOMY. 


many  animals  teeth  have  come  to  be  used  for  purposes 
other  than  those  of  nutrition,  such  as  for  sexual  warfare  ; 
but  it  can  hardly  be  doubted  that  teeth  had  primarily  to 
do  with  the  nourishment  of  their  possessor. 

The  subject  of  the  homologies  of  the  teeth  cannot  be  fully 
entered  upon  until  the  details  of  their  development  have 
been  mastered  ;  still  a  few  words  may  even  at  the  outset  be 
devoted  to  the  elucidation  of  their  real  nature. 

The  mucous  membrane  which  lines  the  alimentary  canal 
is  continuous  with — is,  indeed,  a  part  of — the  external  skin, 
with  which  it  blends  at  the  lips.  Now  if  a  young  dog-fish, 
just  about  to  be  hatched,  be  examined,  it  will  be  found  that 
it  has  no  distinct  under  lip,  but  that  its  skin  turns  in  over 
its  rounded  jaw  without  interruption.  The  skin  outside 
carries  spines  (placoid  scales)^1)  and  these  spines  are  con¬ 
tinued  over  that  part  of  it  which  enters  the  mouth  and 
bends  over  the  jaws  ;  only  they  are  a  little  larger  in  this 
latter  position.  If  the  growth  of  the  dog-fish  be  followed, 
these  spines  of  the  skin  which  cover  the  jaws  become  deve¬ 
loped  to  a  far  greater  size  than  those  outside,  and  the  identity 
and  continuity  of  the  two  become  to  some  extent  masked. 
No  one  can  doubt,  whether  from  the  comparison  of  adult 
forms  or  from  a  study  of  the  development  of  the  parts, 
that  the  teeth  of  the  shark  correspond  to  the  teeth  of  other 
fish,  and  these  again  to  those  of  reptiles  and  mammals ;  it 
may  be  clearly  demonstrated  that  the  teeth  of  the  shark 
are  nothing  more  than  highly  developed  spines  of  the  skin, 
and  therefore  we  infer  that  all  teeth  bear  a  similar  relation 
to  the  skin.  This  is  what  is  meant  when  teeth  are  called 
“dermal  appendages,”  and  are  said  to  be  perfectly  distinct 
from  the  internal  bony  skeleton  of  the  animal ;  the  teeth  of 
the  shark  (and  of  many  other  creatures)  are  not  only  deve- 

P)  “The  placoid  scale  lias  the  structure  of  dentine  ;  is  covered  by 
enamel,  and  is  continued  at  its  base  into  a  plate  formed  of  osseous  tissue.  ” 
Gegenbaur’s  Comparative  Anatomy,  translated  by  F.  Jelfery  Bell,  p.  424. 


THE  TEETH  OF  MAN. 


3 


loped  in  but  always  remain  imbedded  in  tough  mucous 
membrane,  and  never  acquire  any  connection  with  the  bone. 
Indeed,  all  teeth  alike  are  developed  from  a  part  of  the 
mucous  membrane,  and  any  connection  which  they  may 
ultimately  get  with  the  bone  is  a  secondary  matter.  As  it 
has  been  well  expressed  by  Dr.  Harrison  Allen  (£  Anatomy 
of  the  Facial  Region  ’),  “if  the  hairs  of  the  scalp  were  to  be 
inserted  into  the  skull,  or  of  the  moustache  into  the  upper 
jaw,  we  should  express  great  astonishment,  yet  such  an 
-extreme  proposition  is  no  more  remarkable  than  what  is 
seen  to  take  place  in  the  jaws,”  again  “  the  feathers  of 
•certain  birds  making  impressions  on  the  radius,  the  whale¬ 
bone  pendent  from  the  roof  of  the  mouth,  are  examples  of 
this  same  association  of  tegumentary  appendages  with  the 
bones.” 

To  these  may  be  added  the  horny  plates  of  Ornitho¬ 
rhyncus,  which  are  pure  hardenings  of  the  stratum  corneum 
of  the  oral  epithelium,  but  which  have  definite  beds  pro¬ 
vided  for  them  on  the  bones. 

In  their  simpler  forms,  then,  teeth  are  met  with  as  very 
numerous  spines,  differing  but  little  from  the  spines  of  the 
skin  except  in  size,  and  still  less  from  one  another.  In 
many  fish  the  teeth,  though  more  specialised,  are  scattered 
over  almost  every  one  of  the  numerous  bones  which  form 
part  of  the  walls  of  the  mouth  and  pharynx ;  in  reptiles 
they  are  much  more  limited  in  position,  and  in  mammals 
are  absolutely  confined  to  the  intermaxillary,  maxillary, 
and  mandibular  (lower  maxillary)  bones.  In  fish  and  rep¬ 
tiles  it  is  the  exception  for  the  teeth  in  different  parts  of 
the  mouth  to  differ  markedly  from  each  other  ■  in  mam¬ 
mals  it  is  the  rule. 

Teeth  owe  their  hardness  to  an  impregnation  with  salts 
of  lime  ;  the  organic  matrix  may  be  of  albuminoid  character, 
in  which  case  the  tooth  is  of  horny  consistence,  and  is  spoken 
of  as  “  cornified ;  ”  or  the  matrix  may  be,  like  that  of  bone, 


4 


A  MANUAL  OF  DENTAL  ANATOMY. 


gelatigenous,  in  which  case  the  tooth  is  much  more  richly 
impregnated  with  salts,  and  is  spoken  of  as  “  calcified.” 

Horny  teeth,  so  far  as  they  have  been  investigated,  consist 
of  aggregations  of  cells  of  the  stratum  corneum  of  the  oral 
epithelium,  and  they  are  penetrated  on  their  under  side  by 
the  papillae  wdiose  enormously  exaggerated .  epithelial  coats 
have  built  them  up. 

The  great  mass  of  a  calcified  tooth  is  usually  made  up  of 
“dentine,”  which  gives  to  it  its  characteristic  form,  and 
often  practically  constitutes  the  whole  tooth :  to  this  may 
or  may  not  be  added  enamel  and  cementum. 

Without  further  prelude  wTe  may  pass  to  a  description  of 
the  human  teeth,  this  course  appearing  to  me,  after  some 
little  consideration,  to  afford  to  the  student  the  most  ad¬ 
vantageous  introduction  to  the  subject,  as  he  must  neces¬ 
sarily  already  possess  some  knowledge  of  their  forms,  while 
to  the  matters  alluded  to  in  the  preceding  pages  more  full 
reference  will  be  made  hereafter. 

In  the  human  subject  no  tooth  rises  above  the  level  of 
its  fellows,  and  the  teeth  are  arranged  in  close  contact,  with 
no  interspaces  between  them.  The  teeth  are  ranged  around 
the  margins  of  the  jaws  in  a  parabolic  curve,  or  something' 
approximating  to  one ;  in  the  lower  races  of  mankind  the 
curve  tends  to  a  squarish,  oblong  form,  owing  to  the 
prominence  of  the  canines  (compare  the  figure  of  the  denti¬ 
tion  of  Simia  satyrus),  whilst  a  deviation  in  the  opposite 
direction  is  daily  becoming  more  common  in  the  most 
highly  civilised  races,  resulting  in  a  contour  to  which  in 
extreme  cases  the  name  of  Y-shaped  maxilla  is  applied. 

It  may  be  stated,  as  generally  true,  that  the  teeth  are 
somewhat  larger  on  their  labial  than  on  their  lingual  aspect,, 
a  result  which  necessarily  follows  from  their  standing  with¬ 
out  interspaces  along  a  curved  line.  And  as  great  variations- 
in  size  and  shape,  as  well  as  in  colour,  are  found  to  exist 
between  different  individuals,  it  is  only  possible  to  give 


THE  TEETH  OF  MAN. 


5 


such  a  description  as  shall  apply  to  the  generality  of 
teeth. 

The  teeth  of  the  upper  jaw  are  ranged  along  a  curve  of 
larger  dimensions  than  those  of  the  lower,  the  incisors  pass¬ 
ing  in  front  of  the  corresponding  lower  teeth,  and  the 
-external  cnsps  of  the  bicuspids  and  molars  closing  outside 
those  of  the  lower  teeth. 

There  are,  however,  some  points  of  detail  to  be  noted  in 
the  relation  borne  by  the  upper  to  the  lower  teeth,  besides 
that  comprised  in  the  general  statement  that  the  former  lie 
outside  the  latter,  by  which  it  is  brought  about  that  each 
tooth  is  antagonised  by  portions  of  two  teeth  in  the  other 
jaw,  instead  of  having  only  a  single  opponent. 

The  upper  incisors  and  canines,  when  the  mouth  is  closed, 
from  the  larger  size  of  the  arch  in  which  they  are  arranged, 
shut  over  and  in  front  of  the  lower  teeth,  concealing  the 
upper  thirds  of  their  crowns ;  while  the  external  tubercles 
of  the  bicuspids  and  molars  of  the  lower  jaw  are  received 
into  the  depressions  between  the  external  and  internal 
tubercles  of  the  similar  teeth  in  the  upper  jaw,  thus  allow¬ 
ing  the  external  tubercles  of  the  upper  teeth  to  close  ex¬ 
ternally  to  the  outer  tubercles  of  the  lower  row. 

From  this  arrangement  of  the  tubercles,  we  are  enabled 
in  mastication  to  use  the  whole  surface  of  the  crowns  of  the 
opposing  teeth  ;  the  act  of  mastication  being  performed  by 
bringing  the  external  tubercles  of  the  under  molars  opposite 
to  those  of  the  upper  row  ;  whence,  by  the  lateral  motion 
of  the  under  jaw  inwards,  their  external  tubercles  pass  down 
the  inclined  surfaces  of  the  external,  and  up  those  of  the 
internal  tubercles  of  the  upper  teeth,  crushing  in  this  action 
any  interposed  substance. 

It  will  also  be  observed  that,  from  the  difference  of  width 
in  the  incisors  of  the  two  jaws,  the  central  incisors  of  the 
upper  extend  over  the  centrals  and  half  of  the  laterals  of 
the  under  row,  and  that  the  superior  laterals  lie  over  the 


6 


A  MANUAL  OF  DENTAL  ANATOMY. 


remaining  half  of  the  inferior  laterals  and  the  anterior  half  of 
the  canines  of  the  lower  jaw.  The  canines  close  over  the  halves 
of  the  canines  and  first  bicuspids,  while  the  first  bicuspids 
impinge  on  the  half  of  the  first  and  half  of  the  second  bi- 
cuspids  of  the  lower  row.  The  second  upper  bicuspids  close 
upon  the  anterior  third  of  the  opposing  first  molars  and  the 
posterior  half  of  the  second  bicuspids. 

The  first  molars  opjiose  the  posterior  two-thirds  of  the 
first,  and  one  third  of  the  second  molars  of  the  lower  jawy 
while  the  second  upper  molars  close  upon  the  unoccupied 
posterior  third  of  the  second  and  the  anterior  third  of  the 
wisdom  teeth.  The  wisdom  tooth  of  the  upper  being- 
smaller  in  size  than  that  of  the  lower  jaw  is  perfectly 
opposed  by  that  portion  of  the  latter  left  unoccupied  by 
the  second  under  molar  tooth. 

By  this  admirable  arrangement  no  two  teeth  oppose  each 
other  only,  but  each  tooth  in  closure  of  the  jaw  impinges 
upon  two,  so  that  should  a  tooth  be  lost,  or  even  two  alter¬ 
nate  teeth,  still  the  corresponding  teeth  of  the  opposite  jaw 
are  to  some  extent  opposed,  and  thus  remain  useful.  For 
when  a  tooth  is  wholly  unopposed,  a  process  is  apt  to  be 
set  up  in  the  jaw  by  which  the  useless  organ  is  gradually 
ejected.  The  direction  of  the  teeth  in  the  upper  is  vertically 
downwards  and  slightly  forwards,  while  those  of  the  lower 
jaw  are  placed  vertically,  the  molars  tending  slightly  inwards. 

It  is  usual  to  represent  the  dentition  of  any  animal  by 
what  is  termed  a  dental  formula,  which  enables  the  reader 
at  a  glance  to  see  the  number  of  teeth  of  each  variety  pos¬ 
sessed  by  the  creature.  Thus,  instead  of  writing  out  at 
length  that  man  has  two  incisors  on  each  side  in  both  upper 
and  lower  jaws,  one  canine,  two  bicuspids  or  premolars,  &c.y 
it  is  written  thus  : — 


1  2  3 

c.  —  prm.  -  in. 


f 


i 


9 


THE  TEETH  OF  MAN. 


i 


or  in  the  deciduous  set : — 

.21  2 
1.  c.  m.  ~  =  20. 

Z  JL  Z 

For  the  purpose  of  description  three  parts  of  the  tooth 
are  distinguished  by  name,  viz.,  the  crown,  neck,  and  root. 

This  distinction  of  parts  which  we  make  in  describing 
human  teeth,  when  we  speak  of  crown,  neck,  and  root,  is 
applicable  to  the  great  majority  of  mammalian  teeth, 
though  there  are  some  few  simple  forms  of  teeth  in  which 
no  such  differentiation  of  parts  can  be  seen. 

The  crown  is  that  portion  which  is  exposed  above  the 
borders  of  the  gum,  and  is  in  human  teeth  coated  with 
enamel ;  the  neck  is  that  portion  which  corresponds  to  the 
edge  of  the  gum,  and  intervenes  between  the  edges  of  the 
bony  sockets  and  the  edge  of  the  enamel ;  the  root  is  that 
part  which  is  enclosed  within  the  bony  socket,  and  is 
covered  by  cementum. 

Of  these  it  is  to  be  remarked  that  the  “  neck,”  although 
a  convenient  and  necessary  term  for  descriptive  purposes, 
marks  an  .arbitrary  division  of  less  importance  than  that 
expressed  by  crown  and  root ;  also  that  although  this  divi¬ 
sion  into  three  parts  can  be  made  in  the  case  of  socketed 
teeth  of  limited  growth,  no  such  distinction  of  parts  can  be 
made  in  teeth  of  perpetual  growth. 

Special  names  have  been  applied  to  the  various  surfaces 
of  the  crowns,  as,  owing  to  the  curvature  of  the  alveolar 
border,  terms  which  had  reference  to  front,  back,  or  sides 
would,  in  different  parts  of  the  mouth,  indicate  different 
surfaces,  and  so  lead  to  confusion. 

The  lips  and  tongue  and  the  median  line  of  the  mouth, 
however,  are  not  open  to  this  objection,  so  the  surfaces 
which  are  directed  outwards  towards  the  lips  are  called 
“labial;”  and  those  inwards  towards  the  tongue  “lingual;” 
the  interstitial  surfaces  are  called  “  median  ”  and  “  distal,” 


8 


A  MANUAL  OF  DENTAL  ANATOMY . 


the  word  median  being  applied  to  the  surface  which  would 
look  towards  the  middle  line  of  the  mouth  had  the  alveolar 
border  been  straightened  out.  In  other  words  behind  the 
canine,  the  “median”  is  equivalent  to  anterior,  and  “distal  ” 
to  posterior  surface. 

Forms  of  the  several  Teeth. — It  is  usual  to  speak  of 
the  teeth  as  being  modified  cones,  and  to  attribute  their 
variations  to  deviations  from  this  typical  shape.  In  a  broad 
sense  this  maybe  true  of  the  simplest  teeth,  such  as  are  met 
with  in  some  fish  and  reptiles  and  monophyodont  mammals, 
which  are  little  more  than  simple  cones  ;  but  there  are  in¬ 
dications  which  would  point  to  something  more  complex 
than  this  as  a  very  early  form  of  mammalian  tooth,  for  even 
among  the  monophyodonts,  as  I  have  elsewhere  pointed  out, 
the  armadillo  has  a  bilobed  tooth  germ,  the  one  cusp  pre¬ 
dominating  over  the  other.  And  the  teeth  of  the  Ornitho¬ 
rhyncus,  which  from  many  considerations  must  be  regarded 
as  exceedingly  early  forms  of  mammalian  teeth,  were  broad 
topped,  had  on  one  side  somewhat  pronounced  cusp3,  and  on 
the  other  a  crenulated  margin,  and  had  several  short  roots. 
In  Mesozoic  times  most  mammals  had  the  full  typical 
number  of  teeth,  the  molars  were  usually  tuberculated, 
and  in  many  groups  a  very  distinct  series  of  modifications 
from  parent  forms  has  been  traced  out.  Proceeding  from 
these  generalised  forms  the  specialisation  usually  takes 
the  form  of  a  shortening  of  the  length  of  the  jaws,  accom¬ 
panied  by  a  reduction  in  the  number  of  the  teeth,  some 
teeth  being  suppressed  and  others  taking  on  some  particular 
development.  This  specialisation  of  teeth  frequently  goes 
on  hand-in-hand  with  specialisation  of  limbs. 

It  has  been  usual  to  suppose  that  the  teeth  which  are  miss¬ 
ing  in  man  are  the  third  incisor  on  each  side  and  the  first  and 
second  premolars,  but  reasons  have  been  advanced  which 
throw  doubt  upon  this  conclusion  as  regards  the  incisors 
(Albrecht,  Zoolog.  Anzeig .,  1879 ;  Prof.  Sir  W.  Turner,  Journal 


THE  TEETH  OF  MAN . 


9 


of  Anatomy  and  Physiology ,  188 5  ;  A.  Wilson,  BritisJb  Dental 
Association  Journal ,  April,  1885  ;  Edwards,  British  Dental 
Association  Journal ,  December,  1885).  From  the  study  of 
cases  of  cleft  palate  it  has  been  found  that  it  is  not  at  all 
certain  that  the  cleft  usually  runs  along  the  site  of  the 
suture  between  the  intermaxillary  bones  and  the  maxilla, 
for  it  often  appears  to  be  well  within  the  limits  of  the 
intermaxillary  bone,  and  so  lends  some  support  to  the  idea 
of  Albrecht  that  there  are  two  intermaxillary  bones  on  each 
side,  and  that  the  cleft  runs  along  the  division  between 
them.  And  it  is  far  from  uncommon  for  a  tooth  of  incisor 
type  to  lie  beyond  the  cleft  and  close  against  the  front  of 
the  canine ;  to  this  tooth  Sir  W.  Turner,  pending  decision 
as  to  its  homologies,  gives  the  name  of  precanine.  The 
argument  put  briefly  is  this  ;  a  tooth  outside  the  cleft  and 
close  to  the  canine  is  so  common  of  occurrence  that  its 
position  there  must  be  due  to  something  other  than  accident, 
the  normal  number  of  incisors  not  being  exceeded.  But 
there  is  a  case  on  record  in  which  this  precanine  existed 
although  there  were  four  incisors  upon  the  intermaxillary 
portion,  which  was  isolated  by  a  double  cleft;  in  this 
specimen  therefore  the  precanine  was  evidently  i3  of  the 
normal  mammalian  dentition,  and  it  is  therefore  not  unlikely 
that  it  is  always  so  ;  if  this  inference  be  correct,  then  the 
lost  incisor  in  man  is  probably  i2. 

I  do  not  think  that  we  have  at  present  the  data  upon  which 
to  certainly  determine  the  fundamental  form  of  the  mamma¬ 
lian  tooth,  but  there  is  evidence  that  all  the  teeth  in  the  jaw  of 
a  mammal  may  have  been  derived  from  a  common  form  ;  in 
other  wrords,  marked  though  the  distinction  between  incisors, 
canines,  bicuspids,  and  molars  seems  to  be  at  first  sight,  a 
closer  inspection  reveals  various  gradational  or  transitional 
characters  linking  them  together,  though  there  are  gaps  in 
the  chain  not  bridged  over  by  forms  knowm  to  us.  This 
may  be  seen  by  a  careful  study  of  the  human  teeth,  as  I 


10 


A  MAX  UAL  OF  DENTAL  ANATOMY . 


shall  endeavour  to  show ;  but  it  is  much  more  conspicuously 
seen  in  an  extinct  animal  (Homalodontotherium,  an  extinct 
ungulate  from  Patagonia,  described  by  Professor  Flower, 
Philos,  Trans.  1874),  which  apparently  possessed  the  full 
typical  number  of  mammalian  teeth,  viz.,  forty-four.  The 
point  in  which  its  dentition  is  chiefly  instructive  is  that  the 
teeth,  in  close  juxtaposition  one  with  another,  present  an 
exceedingly  perfect  gradation  of  form  from  the  front  to  the 
back  of  the  mouth,  no  tooth  differing  markedly  from  its 
neighbour,  though  the  difference  between,  say,  the  first 
incisor  and  first  molar,  is  exceedingly  great.  In  Professor 
Flower’s  words,  “  it  is  only  by  the  analogy  of  other  forms 
that  they  can  be  separated  into  the  groups  convenient  for 
descriptive  purposes,  designated  as  incisors,  canines,  premo- 
lars,  and  molars.” 

In  viewing  the  gradational  characters  which  do  exist  be¬ 
tween  the  various  human  teeth,  it  must  not  be  forgotten 


that  some  links  in  the  chain  have  dropped  out  and  are 
absent.  Mention  has  already  been  made  of  the  full  typical 
number  of  mammalian  teeth  being  44,  i.e. 


.  3  1  4  3 

l.  -  c.  -  prm.  -  m.  —  =  44 

o  1  4  o 

Incisors. — Of  these  there  are  four  in  each  jaw  ;  two  cen¬ 

tral,  two  lateral  incisors.  Their  working  surfaces  form 
wedges,  or  obtuse  and  blunt-edged  chisels,  calculated  to 
divide  food  of  moderate  consistency. 

Upper  Incisors. — The  centrals  are  very  much  larger 
than  the  laterals,  and  viewed  either  from  the  back  or  front 
taper  with  some  regularity  from  the  cutting  edge  to  the 
point  of  the  root,  the  neck  not  being  marked  by  strong  con¬ 
striction.  The  crown  of  the  tooth,  as  seen  from  the  front,  is. 
squarish,  or  more  strictly,  oblong,  its  length  being  greater 
than  its  breadth. 

The  median  side,  by  which  it  is  in  contact  with  its  fellow. 


THE  TEETH  OF  MAH. 


11 


is  a  little  longer  than  the  distal,  so  that  the  median  angle  of 
the  crown  is  a  little  lower,  and,  as  a  necessary  consequence, 
a  little  more  acute  than  the  distal  angle  of  the  cutting  edge. 
Near  to  their  base  the  crowns  narrow  rather  abruptly,  so 


Fig.  lb). 


that  at  the  neck  a  space  is  left  between  the  contiguous 
teeth. 

The  labial  surface  is  slightly  convex  in  each  direction,  and 
often  presents  slight  longitudinal  depressions,  which  end  at 
the  cutting  edge  in  slight  notches. 

In  recently-cut.  teeth  the  thin  cutting  edge  is  elevated  into 
three  slight  cusps,  which  soon  wear  down  and  disappear  after 
the  tooth  has  been  in  use. 

V 

The  edge  of  an  incisor  may  be  regarded  as  formed  by  the 
bevelling  off  of  the  dentine  of  the  lingual  surface,  which  is 
nearly  flat  from  side  lo  side,  with  a  slight  tendency  to  con¬ 
cavity,  while  from  above  downwards  it  is  distinctly  concave, 
and  often  presents  longitudinal  depressions  similar  to  those 
on  the  labial  surface.  The  lingual  surface  towards  the  gum 
terminates  in  a  distinct  prominence,  oftentimes  amounting 
to  a  bounding  ring  of  enamel,  termed  the  basal  ridge ,  or,  in 
the  language  of  comparative  anatomy,  the  cingulum.  It  is 
variable  in  the  extent  of  its  development ;  it  rarely  rises 


(l)  Front  and  side  view  of  a  left  upper  central  incisor. 
a  Distal  surface.  b  Neck.  c  Foot. 


12 


A  MANUAL  OF  DENTAL  ANATOMY 


into  a  central  prominence  at  the  back,  but  in  the  angle 
where  the  ridges  of  the  two  sides  meet  a  deep  pit  is  often 
left  in  the  enamel,  which  is  a  favourite  site  for  caries.  The 
crown,  or  what  amounts  to  the  same  thing,  the  enamel,  ter¬ 
minates  on  the  lingual  and  labial  aspect  of  the  tooth  in  a 
curved  line,  the  convexity  of  the  curve  being  directed 
upwards  towards  the  gum  ;  on  the  interstitial  surfaces, 
both  median  and  distal,  the  curve  is  less  regular,  and  its 
contour  would  be  more  correctly  described  as  Y-shaped,  the 
apex  of  the  Y  being  towards  the  crown  of  the  tooth  and 
away  from  the  gum.  The  dentist  will  do  well  to  remember 
the  disposition  of  the  enamel  in  this  situation,  as  it  is  a 
point  of  some  importance  in  shaping  the  cervical  edge  of  a 
cavity  preparatory  to  filling  it. 

The  transverse  indentations  of  the  enamel  met  with  both 
on  lingual  and  labial  surfaces,  though  more  especially  in  the 
latter,  are  marks  of  arrest  of  development,  and,  common  as 
they  are,  are  to  be  regarded  as  abnormalities. 

The  central  incisors  are  larger  than  the  laterals,  though 
not  in  so  great  degree  as  is  the  case  in  the  anthropoid 
apes. 

The  pulp  cavity  bears  a  general  resemblance  to  the  ex¬ 
ternal  contour  of  the  tooth  ;  towards  the  cutting  edge  it  is 
very  thin,  and  is  prolonged  at  its  two  corners  to  a  slight 
extent  into  “cornua;”  at  the  neck  it  is  cylindrical,  and  is 
also  cylindrical  in  the  root,  tapering  gradually  till  it  ap¬ 
proaches  close  to  the  apex,  when  it  becomes  suddenly  con¬ 
stricted. 

Upper  lateral  incisors  are  in  every  dimension  some¬ 
what  smaller  than  the  centrals.  They  widen  somewdiat 
abruptly  near  to  the  cutting  edge,  but  below  this  they  taper 
pretty  regularly  to  the  end  of  the  root ;  the  labial  surface 
is  convex  in  each  direction,  while  the  lingual  surface  is 
perhaps  rather  flatter  than  that  of  a  central  incisor. 

The  outer  (distal)  angle  of  the  crown  is  far  more  rounded 


THE  TEETH  OF  MAN. 


13 


or  sloped  away  than  in  the  centrals,  and  the  distal  surface, 
looking  towards  the  canine,  is  in  a  slight  degree  convex;  the 
median  surface  may  be  slightly  concave. 


Fig.  2  (L). 


The  enamel  terminates  towards  the  gum  in  contours  pre¬ 
cisely  similar  to  those  which  obtain  in  the  centrals :  but 
the  basal  ridge,  or  cingulum,  is  often  more  strongly  pro¬ 
nounced,  and  the  presence  of  a  central  tubercle  upon  it  is 
less  infrequent.  From  this  greater  prominence  of  the  cin¬ 
gulum  and  Consequent  more  marked  depression  in  front  of 
it,  caries  is  more  frequent  upon  the  lingual  surfaces  of  upper 
lateral  than  upon  those  of  upper  central  incisors. 

The  pulp  cavity  is,  relatively  to  the  whole  tooth,  perhaps 
a  little  larger  than  in  the  central  incisors  ;  in  other  respects 
the  same  description  will  suffice. 

Lower  central  incisors  are  very  much  narrower  than 
those  of  the  upper  jaw  ;  not  more  than  half  the  width  at 
their  cutting  edges,  which  again  are  much  wdder  than  the 
necks  of  the  teeth. 

From  before  backwards  they  are  deep  at  the  neck  ;  hence 
the  fangs  are  very  much  flattened  from  side  to  side,  and 
rotation  is  inadmissible  in  the  attempt  to  extract  them. 

The  enamel  contour  at  the  neck  is  similar  to  that  of  the 
upper  incisors,  but  there  is  no  well-marked  cingulum. 

Lower  lateral  incisors  are,  unlike  the  upper  teeth,  dis¬ 
tinctly  larger  than  the  centrals  in  each  one  of  their  dimen- 


fl)  Front  and  side  view  of  a  left  upper  lateral  incisor. 


14 


A  MANUAL  OF  DENTAL  ANATOMY. 


sions,  but  more  especially  in  the  length  of  their  fangs, 
which  are  much  flattened,  and  often  present  on  their  sides 
a  median  longitudinal  depression,  sometimes  amounting  to 
an  actual  groove. 

Fig.  3  0. 


The  distal  angle  of  the  crown  is  rounded  off  like  that  of 
the  upper  lateral  incisors,  though  not  so  markedly. 

Canines,  Cuspidati,  Eye  Teeth,  are,  in  all  respects, 
stouter  teeth  than  the  incisors  ;  not  only  are  the  crowns 
thicker  and  stronger,  but  the  roots  are  very  much  longer. 

The  crown  terminates  in  a  blunt  point,  which  lies  in  a 
straight  line  with  the  long  axis  of  the  root ;  a  feebly  pro¬ 
nounced  line  or  ridge  runs  down  the  outer  surface  of  the 
tooth  from  this  point  to  the  neck.  The  crown  slopes  away 
both  before  and  behind  the  point  or  cusp,  but  as  that  side 
of  the  tooth  which  lies  next  to  the  bicuspid  is  convex,  and 
as  it  were  produced  towards  that  tooth,  the  slope  is  longer 
on  the  distal  than  on  the  mesial  half  of  the  crown.  The 
crown  thus  not  being  perfectly  symmetrical  renders  it  easy 
to  determine  at  a  glance  to  which  side  of  the  mouth  the 
canine  belongs. 

The  internal  or  lingual  surface  is  not  concave  like  that  of 
the  incisors,  but  is  in  a  slight  degree  convex,  and  a  median 
ridge  runs  down  it  from  the  apex  of  the  cusp  ;  this  ridge 
where  it  meets  with  the  ridge  which  borders  the  lingual 
surface  and  corresponds  with  the  cingulum  of  the  incisor 


0  Front  and  side  view  of  lower  central  incisor. 


THE  TEETH  OF  MAN. 


15 


teeth,  is  often  developed  into  a  well-marked  prominence  or 
cusp. 

In  transverse  section  the  neck  is  nearly  triangular,  the 
outer  or  labial  being  much  wider  than  the  lingual  aspect. 
Lower  canines  are  less  pronounced  in  form  than  the  cor- 


Fig.  4  (1). 


responding  upper  teeth :  the  point  is  more  blunted,  the 
fang  shorter,  the  perpendicular  labial  ridge  not  being 
traceable,  and  the  want  of  symmetry  between  the  mesial 
and  distal  halves  of  the  crown  less  marked.  The  lingual 
surface  has  perhaps  a  greater  tendency  to  concavity. 

Premolars,  Bicuspids,  are  eight  in  number,  two  on  each 
side  of  both  upper  and  lower  jaws,  and  they  correspond  to 
the  third  and  fourth  premolars  of  the  typical  mammalian 
dentition,  the  first  and  second  premolars  not  being  repre¬ 
sented  in  man  (2). 

Upper  Premolars. — The  crown,  as  seen  looking  upon 
its  grinding  surface,  is  roughly  quadrilateral,  its  outer  or 
labial  border  being,  however,  larger  and  thicker  than  its 
inner,  and  the  teeth  are  carried  round  the  curve  of  the 
alveolar  border  mainly  by  means  of  this  difference  in  size 
in  the  external  and  internal  portions  of  the  canines  and  the 
two  bicuspids. 

(b  Lingual,  labial,  and  distal  surfaces  of  an  upper  canine,  showing  the 
basal  cusp  and  the  three  ridges  which  converge  towards  it. 

(2)  Mr.  A.  Wilson  holds  that  prm1  and  prm4  have  disappeared. 


16 


A  MANUAL  OF  DENTAL  ANATOMY. 


As  is  implied  by  its  name,  the  crown  has  two  cusps,  of 
which  the  outer  is  the  larger  and  stouter,  and  broader. 
The  outer  and  inner  surfaces  (labial  and  lingual)  are  convex 
and  smooth,  with  no  basal  ridges  at  the  edge  of  the  gums. 
The  inner  and  outer  cusps  are  not  joined  by  a  transverse 


Fig.  5  (*). 


ridge  ;  instead  of  this  there  is  a  deep  transverse  (concave  to¬ 
wards  labial  side)  fissure ;  in  point  of  fact  the  cingulum  has 
been  elevated  to  form  the  inner  cusp,  and  forms  slight  ele¬ 
vations  bordering  the  anterior  and  posterior  (median  and 
distal)  edges  of  the  grinding  surface.  The  median  surface, 
where  it  fits  against  the  canine,  is  concave. 

The  root  is  single,  and  much  compressed  from  side  to 
side  :  very  often,  however,  it  is  double  for  the  greater  part 
of  its  length,  and  if  not  so  divided  is  often  marked  by  a 
groove  upon  each  side  indicating  a  tendency  towards  such 
division.  The  outer  border  of  the  root  is  also  often 
marked  by  a  longitudinal  furrow,  which  may  amount  to 
complete  division.  In  fact  a  bicuspid  may  have  three 
perfectly  distinct  roots,  like  a  molar,  and  like  the  premolars 
of  monkeys,  in  which  three  is  the  normal  number  of  roots. 
The  first  bicuspid  is  more  variable  in  respect  of  its  roots 
than  the  second. 

The  second  upper  bicuspid  differs  from  the  first  in  that 
the  difference  in  size  between  its  outer  and  inner  cusps  is 
less,  the  inner  cusp  being  relatively  considerably  larger, 
and,  indeed,  often  preponderating  over  the  labial  cusp  in 
length,  so  that  the  labial  and  lingual  surfaces  are  nearly 
equal. 

f1)  Grinding  surface  of  an  upper  bicuspid. 


THE  TEETH  OF  MAN. 


17 


The  pulp  cavity  in  the  crown  is  furnished  with  distinct 
cornua  ;  at  the  neck  it  is  very  much  flattened  from  side  to 
side,  being  often  reduced  to  a  mere  fissure,  which  is  how¬ 
ever  considerably  larger  at  its  two  extremities  than  in  its 
middle.  Hence  the  pulp  cavity  of  an  upper  bicuspid  is 
difficult  to  fill ;  a  difficulty  again  increased  by  the  impos¬ 
sibility  of  always  discovering  what  number  of  fangs  it  has, 
as  their  division  sometimes  takes  place  rather  high  up. 

Lower  premolars  are  smaller  teeth  than  those  of  the 
upper  jaw,  and  are  quite  distinct  in  shape.  The  outer  or 
labial  cusp  is  bent  inwards,  and  the  labial  surface  of  the 
crown  is  very  convex.  The  inner  cusp  is  but  feebly  deve¬ 
loped,  and  is  connected  with  the  outer  by  a  low  ridge  ;  it  is 
also  narrow. 

The  root  is  rounded,  a  little  larger  on  its  outer  side  than 
on  its  inner,  and  tapers  regularly  towards  its  point ;  the 
pulp  cavity  is  cylindrical  at  the  neck,  and  also  tapers  regu¬ 
larly  in  the  root.  The  cornu  of  the  pulp  which  corresponds 
to  the  inner  cusp  is  but  feebly  developed. 

The  second  lower  bicuspid  differs  a  good  deal  from  the 
first ;  its  crown  is  much  squarer  and  larger  in  all  its  dimen¬ 
sions.  The  inner  cusp  reaches  to  a  higher  level  and  is 
stouter,  and  the  greater  development  of  the  ridge  which 
bounds  the  posterior  (distal)  border  of  the  grinding  surface 
makes  it  attain  to  such  a  large  size  as  to  make  the  tendency 
towards  a  transition  from  the  bicuspid  type  to  the  quadri- 
cuspid  type  of  a  true  molar  very  evident.  It  is  rare  for  any 
tendency  for  a  division  into  two  roots  to  be  met  with ;  when 
it  does  occur  it  bears  a  curious  similarity  to  the  form  of 
root  met  with  in  the  anthropoid  apes  (cf.  the  chapter 
relating  to  the  teeth  of  monkeys). 

The  differences  between  a  well-marked  incisor,  canine,  or 
premolar  are  so  strongly  pronounced  that  the  resemblances 
which  underlie  them  are  apt  to  be  overlooked. 

Nevertheless  a  very  distinct  gradation  may  be  traced,  and 


18 


A  MANUAL  OF  DENTAL  ANATOMY. 


it  is  far  from  uncommon  to  meet  with  teeth  which  possess 
in  a  marked  degree  transitional  characters.  If  the  external 
or  distal  angle  of  a  lateral  incisor  be  sloped  off  more  than 
usual,  while  at  the  same  time  its  cingulum  and  basal  pro- 

Fig.  6  (’l). 


minence  be  wTell  marked,  it  makes  no  bad  imitation  of  a 
diminutive  canine ;  and  such  laterals  are  often  to  be  met 
with  by  any  who  search  for  such  deviations  from  the  normal 
form. 

Thus  the  form  characteristic  of  a  lateral  incisor,  if  it  be  a 
little  exaggerated,  very  nearly  gives  us  the  form  of  a  canine, 
and  if  we  look  at  the  teeth  of  an  Orang  the  lateral  incisor  is 
to  all  intents  a  diminutive  canine ;  and  in  the  present  dis¬ 
cussion  the  great  comparative  size  of  the  canine,  which  is 
traceable  to  readily  intelligible  causes,  may  be  put  aside,  as 
it  tends  to  obscure  the  point  to  be  here  insisted  on. 

Between  the  canines  and  the  bicuspids  a  similar  relation¬ 
ship  in  form  exists,  and  it  is  more  apparent  in  the  lower 
than  in  the  upper  jaw.  The  fact  that  at  the  base  of  the 
inner  or  lingual  aspect  of  the  canine  is  to  be  found  an 
elevation  of  the  cingulum,  in  many  instances  amounting  to 
a  low  cusp,  has  been  already  noted ;  and  it  has  already  been 
pointed  out  that  the  inner  cusp  of  the  first  lower  bicuspid  is 
both  smaller  and  lower  than  the  outer.  A  longitudinal 
section  through  the  crowns  of  the  two  teeth  will  demon¬ 
ic1)  Lower  first  bicuspid,  seen  from  the  inner  side,  and  showing  the  pre¬ 
ponderance  of  its  outer  over  its  inner  cusp. 


THE  TEETH  OF  MAN. 


19. 


strate  without  the  necessity  of  further  description  that  the 
basal  cusp  of  the  canine  and  the  inner  cusp  of  the  bicuspid 
are  the  same  thing,  differing  only  in  degree,  while  it  is 
interesting  to  note  that  the  pulp  chamber  in  the  bicuspid 
has  hardly  any  prolongation  towards  the  small  inner  cusp, 
so  that  the  resemblance  between  the  two  teeth  is  thus  made 
more  complete. 

This  close  relationship  of  canines  and  bicuspids  will  be 

Figs.  7  l1). 


again  considered  in  the  chapter  on  the  Homologies  of  the 
Teeth  ;  for  our  present  purpose  it  will  suffice  to  merely  point 
out  its  existence.  The  transition  from  the  bicuspids  to  the 
molars  is  more  abrupt ;  at  least  it  is  not  so  easy  to  point 
out  exactly  how  a  modification  of  the  one  would  arrive  at 
the  form  of  the  other.  But  it  merely  needs  an  exaggera¬ 
tion  of  the  differences  existing  between  a  canine  and  a  first 
bicuspid  to  make  a  good  imitation  of  a  second  bicuspid. 

If  any  one  will  take  the  trouble  to  make  mental  note  of 
the  deviation  in  form  which  he  meets  with  in  teeth,  he  will 
find  that  they  almost  invariably  consist  of  approaches  to¬ 
wards  the  form  of  the  teeth  on  either  side  of  them ;  and 
will  infallibly  be  led  to  the  conclusion  that  incisors,  canines, 
and  bicuspids  are  not  three  patterns  of  teeth  perfectly 


(J)  Section  of  a  lower  canine  and  first  bicuspid,  showing  the  characters 
common  to  the  two. 


c  2 


20 


A  MANUAL  OF  DENTAL  ANATOMY. 


distinct,  and  each  sui  generis ,  but  that  they  are  modifications 
of  one  and  the  same  pattern.  I  may  add,  that  comparati  ve 
odontology  teaches  us  the  same  thing,  and  demonstrates 
clearly  the  substantial  identity  of  the  three  forms,  as  also  of 
the  true  molars. 

Upper  molar  teeth  have  crowns  of  squarish  form,  the 
angles  being  much  rounded  off.  It  may  be  premised  that 
the  first  molar  is  more  constant  in  shape  than  the  second, 
and  this  latter  than  the  third  ;  with  this  proviso  the  first 
and  second  may  be  described  together. 

The  masticating  surface  carries  four  subequal  cusps,  two 
labial  or  external  and  two  lingual  or  internal ;  the  anterior 
internal  cusp  is  distinctly  the  largest,  and  it  is  connected 
with  the  posterior  external  cusp  by  a  thick  oblique  ridge 
of  enamel,  the  remaining  two  cusps  having  no  such  con¬ 
nection. 

This  oblique  ridge  on  the  upper  molars  is  met  with  in  man, 
the  anthropoid  apes,  and  certain  New  World  monkeys. 

The  grooves  which  separate  the  cusps  pass  down  on  to 
the  labial  and  lingual  surfaces  of  the  crown,  but  are  lost 


Fig.  8  (*). 


before  reaching  the  gum  ;  where  they  terminate,  however, 
there  is  often  a  pit,  which  is  a  very  favourite  situation  for 
caries,  especially  on  the  labial  aspect  of  the  teeth.  It  is 
very  rare  to  see  the  grooves  passing  down  upon  the  mesial 
or  distal  surfaces  of  the  crown,  a  raised  border  of  enamel 
generally  cutting  them  short  in  this  direction. 

(*)  Masticating  surface  of  a  first  upper  molar  of  the  left  side  ;  the 
oblique  ridge  connects  the  anterior  internal  with  the  posterior  external 
cusp. 


THE  TEETH  OF  MAN. 


21 


The  roots  are  three  in  number,  two  external  or  labial,  and 
one  internal  or  palatal.  The  latter  is  the  largest,  and  runs 
in  a  direction  more  strongly  divergent  from  the  axis  of  the 
crown  than  the  other  roots.  It  is  directed  obliquely  in¬ 
wards  towards  the  roof  of  the  palate,  is  subcylindrical,  and 
often  curved. 

The  external  roots  are  less  cylindrical,  being  mutually 
compressed,  so  that  their  largest  diameter  is  transverse  to 
the  dental  arch  ;  the  anterior  is  rather  the  larger  of  the  two, 
and  is  more  strongly  pronounced  on  the  side  of  the  neck  of 
the  tooth.  The  anterior  labial  root  is  occasionally  confluent 
with  the  palatine  root,  but  still  more  frequently  the  pos¬ 
terior  labial  and  palatine  roots  are  confluent :  occasionally, 
also,  four  distinct  roots  may  be  met  with. 

Third  molars,  dentes  sapientice,  wisdom  teeth,  of  the  upper 
jaw,  resemble  in  a  general  way  the  first  and  second  molars  ; 
that  is,  when  they  are  well  developed  and  placed  in  a  roomy 
dental  arch.  But  amongst  more  civilised  races  it  may 
almost  be  said  to  be  exceptional  for  the  wisdom  teeth  to  be 
regular  either  in  form  or  position,  so  that  extreme  variability 
prevails  among  these  teeth. 

The  two  inner  tubercles  are  often  blended  together  and 
the  roots  confluent,  forming  an  abruptly  tapering  cone,  the 
apex  of  which  is  often  bent  and  crooked,  so  that  but  little 
vestige  of  the  three  roots  can  be  traced,  the  pulp  cavity  even 
being  quite  single. 

Lower  molars. — The  first  lower  molar  is  the  most  con¬ 
stant  in  form,  and  is  somewhat  the  largest ;  its  grinding 
surface  presents  five  cusps. 

Four  cusps  are  placed  regularly  at  the  four  corners  of  a 
square,  these  being  divided  from  one  another  by  a  crucial 
fissure ;  the  posterior  arm  of  the  crucial  fissure  bifurcates, 
and  between  its  diverging  arms  is  the  fifth  cusp,  which  is 
thus  in  the  middle  line  and  posterior. 

The  transverse  fissure  passes  over  the  limits  of  the  grind- 


22 


A  MANUAL  OF  DENTAL  ANATOMY. 


ing  surface,  and  on  the  outside  or  labial  surface  of  the  tooth 
ends  in  a  pit,  which  is  a  common  site  for  caries ;  although  it 
occasionally  passes  over  the  lingual  surface,  it  is  here  less 
pronounced.  They  are  implanted  by  two  fangs,  placed 


Fig.  9  i1). 


anteriorly  and  posteriorly ;  the  roots  are  much  flattened 
from  before  backwards,  and  they  are  very  usually  curved 
slightly  backwards.  In  the  median  line  of  each  root  there 
is  usually  a  groove,  by  the  deepening  of  which  four  fangs 
may  be  produced  ;  or  this  may  happen  with  the  one  root 
only,  so  that  a  three-rooted  tooth  is  the  result. 


Fig.  10  (2). 


The  second  molar  does  not  greatly  differ  from  fhe  first 
save  that  the  roots  are  more  often  confluent,  and  the  fifth 
cusp  less  marked,  even  if  it  exists  at  all. 

(!)  Masticating  surface  of  a  first  lower  molar,  right  side,  the  five  cusps 
of  which  are  indicated  by  figures. 

(2)  Second  lower  molar  of  right  side,  the  four  cusps  being  indicated  by 
■figures. 


23 


THE  TEETH  OF  MAH. 


Third  lower  molar. — This  tooth  is  seldom  so  small  as 
the  corresponding  upper  tooth,  and  its  crown  is  often  large 
even  when  its  roots  are  very  stunted.  It  has  five  cusps  as 
a  rule,  and  bears  a  more  or  less  close  resemblance  to  the 
molars  which  precede  it.  It  is  either  two-rooted,  or  if  the 
roots  be  confluent,  a  groove  usually  marks  a  tendency  to 
division  into  two  fangs. 

It  is  stated  by  Prof.  Owen  (“  Odontography,”  page  454), 
that  although  the  wisdom  tooth  is  the  smallest  of  the  three 
molars,  the  difference  is  less  marked  in  the  Melanian  than  in 
the  Caucasian  races,  adding  also  that  the  triple  implantation 
of  the  upper  and  the  double  implantation  of  the  lower  is 
constant  in  the  former  races.  More  extended  observations 
have  overthrown  this  statement  as  a  positive  dictum  to  be 
accepted  without  exceptions,  but  it  may  nevertheless  be 
taken  as  expressing  a  general  truth. 


Fig.  11  P). 


The  milk  teeth  differ  from  the  permanent  teeth  by  being 
smaller,  and  having  the  enamel  terminating  at  the  neck 
with  a  thick  edge,  so  that  the  neck  is  more  distinctly  con¬ 
stricted.  The  incisors  and  canines  are  somewhat  similar  to 
their  successors,  the  canines,  however,  being  relatively  shorter 
and  broader  than  their  successors.  The  first  upper  molars 
have  three  cusps,  two  external  and  one  internal  :  the  second 
more  nearly  resemble  the  permanent  molars. 


f1)  Third  lower  molar  of  the  left  side. 


24 


A  MANUAL  OF  DENTAL  ANATOMY. 


The  second  lower  deciduous  molar  has  four  cusps  and 
resembles  a  second  lower  permanent  molar.  The  roots  of 
the  deciduous  teeth  diverge  from  the  neck  at  greater  angles 
than  those  of  permanent  teeth,  in  consequence  of  their  more 
or  less  completely  enclosing  between  them  the  crypts  in 
which  the  latter  are  developing. 


CHAPTER  II. 


THE  MAXILLARY  BONES. 

The  teeth  are  implanted  in  bone  specially  developed  for 
the  purpose  ;  they  lay  at  the  period  of  their  eruption  in  a 
wide  excavation  in  the  bone  in  which  they  were  free  to 
move  under  the  influence  of  very  slight  forces,  and  the  hone 
in  which  they  are  held  was  moulded  around  their  roots  sub¬ 
sequently  to  their  being  formed  and  moved  into  position. 

The  manner  of  attachment  of  the  human  teeth  is  that 
termed  “  gomphosis,”  i.e.,  an  attachment  comparable  to  the 
fitting  of  a  peg  into  a  hole  ;  the  bony  sockets,  however, 
allow  of  a  considerable  degree  of  motion,  as  may  be  seen  by 
examining  the  teeth  in  a  dried  skull,  the  fitting  being  in 
the  fresh  state  completed  by  the  interposition  of  the  dense 
periosteum  of  the  socket.  This  latter,  by  its  elasticity, 
allows  of  a  small  degree  of  motion  in  the  tooth,  and  so 
doubtless  diminishes  the  shock  which  would  be  occasioned 
by  mastication  were  the  teeth  perfectly  immovable  and 
without  a  yielding  lining  within  their  bony  sockets.  When 
this  becomes  inflamed  and  swollen  by  exudation  the  tooth  is 
pushed  to  a  certain  extent  out  of  the  socket,  and  so  being 
to  a  less  extent  limited  in  its  range  by  the  bony  socket, 
acquires  an  increased  mobility. 

The  teeth  are  in  all  mammalia  confined  to  the  bones  which 
carry  them  in  man,  namely,  the  intermaxillary  and  maxillary 
bones  and  the  lower  maxillary  bone  or  mandible. 


26 


A  MANUAL  OF  DENTAL  ANATOMY. 


While  full  description  of  these  bones  (x)  will  be  found  in  any 
general  anatomical  work,  there  are  a  few  points  in  their 
anatomy  which  directly  concern  the  dental  student,  so  that 
a  brief  enumeration  of  some  of  their  relations  can  hardly  be 
dispensed  with. 

Superior  maxillary  bone. — To  facilitate  description  of 
its  parts,  anatomists  divide  it  into  a  “  body  ”  and  “  pro¬ 
cesses,”  of  which  latter  there  are  four,  the  nasal,  malar, 
alveolar,  and  palatine.  As  the  body  of  the  bone  is  hollowed 
out  by  an  air  cavity,  the  antrum,  its  shape  is  similar  to  that 
of  that  cavity,  namely,  roughly  pyramidal,  the  base  of  the 
pyramid  being  inwards  towards  the  nasal  chamber. 

The  nasal  process  springs  directly  upwards  from  the  body 
in  a  vertical  line  with  the  canine  tooth  :  it  is  a  strong  plate 
of  bone,  roughly  triangular  when  viewed  from  the  side. 

The  malar  process  forms  the  apical  portion  of  the  pyramid 
already  alluded  to  ;  it  starts  out  nearly  horizontally  from 
the  body  just  behind  and  below  the  nasal  process,  and  is 
characterized  by  its  great  strength  and  stoutness.  Never¬ 
theless  it  has  been  known  to  be  fractured  by  a  blow,  and 
separated  from  the  body  of  the  bone.  The  antrum  may  be 
prolonged  into  it. 

The  palatine  process  forms  a  horizontal  table  projecting 
inwards  from  the  body  ;  as  the  floor  of  the  nose  is  nearly  flat, 
and  the  palate  is  arched  from  before  backwards,  the  front  of 
the  palatine  process  is  necessarily  much  thicker  than  the 
back,  where  it  is  quite  a  thin  plate. 

The  alveolar  process  is  a  strong  wide  ridge  of  bone,  curved 
so  as  to  form  with  that  of  the  other  maxillary  bone  the 
elliptical  figure  characteristic  of  the  dental  arch  in  the  higher 
races.  It  may  be  described  as  consisting  of  two  plates,  an 
outer  and  an  inner,  which  are  connected  by  numerous  trans- 

(b  Much  that  is  of  great  interest,  and  that  is  not  to  he  found  in  text 
hooks,  is  embodied  in  a  series  of  papers  on  “The  Facial  Region,”  by 
Dr.  Harrison  Allen  (American  Dental  Cosmos,  1873-74). 


THE  MAXILLARY  BONES. 


27 


verse  septa,  the  sockets  of  the  teeth  being  formed  by  the 
interspaces  between  these  septa.  The  internal  alveolar 
plate  is  the  stronger,  the  external  the  thinner  and  weaker, 
a  fact  of  which  we  take  advantage  when  we  extract  a 
tooth  by  bending  it  slightly  outwards.  On  the  outer  sur¬ 
face  of  the  alveolar  process  ere  eminences  corresponding  to 
the  roots  of  the  teeth,  and  depressions  in  their  interspaces, 


Fig.  12  (1). 


apt  to  be  especially  marked  over  the  canine  teeth ;  while 
between  the  teeth  the  alveolar  processes  attain  to  a  lower 
level,  so  that  the  margins  of  the  bone  are  festooned. 
Looking  down  into  an  empty  socket,  the  bone  is  seen  to 
be  everywhere  very  porous,  and  to  be  perforated  by  foramina 
of  considerable  size,  while  at  the  bottom  there  is  the 
larger  foramen  admitting  the  vessels  and  nerves  of  the 
tooth. 

The  alveolus  of  each  individual  tooth  consists  of  a  shell 
of  comparatively  dense  bone  of  small  thickness,  which  is 
imbedded  in  a  mass  of  loose  spongy  bone ;  this  dense  shell 
comes  into  relation  with  the  dense  cortical  bone  of  the 

(])  Superior  Maxillary  Bone  of  right  side.  1.  Body.  2.  Tuberosity. 
7.  Malar  process.  8.  Nasal  process.  12.  Alveolar  process. 


23 


A  MANUAL  OF  DENTAL  ANATOMY. 


jaw  mainly  at  its  free  margin,  near  to  the  neck  of  the 
tooth.  Over  very  prominent  roots  a  portion  of  alveolus  is 
at  times  wanting,  so  that  in  a  macerated  skull  the  root  is 
exposed  to  view. 

The  upper  maxilla  serves  to  give  form  and  support  to 
the  soft  parts  of  the  face,  and  also  to  carry  the  upper 
teeth.  These  have  to  be  rigidly  fixed,  while  the  teeth 
of  the  lower  jaw  are  brought  forcibly  against  them  with 
more  or  less  of  shock.  And  whilst  these  blows  have  to  be 
received,  and  resisted,  and  ultimately  borne  by  the  cranium, 
it  is  obviously  desirable  that  they  should  be  distributed 
over  a  sufficiently  wide  area,  so  as  not  to  be  felt  un¬ 
pleasantly. 

The  ascending  nasal  process  is  very  stout,  and  serves  to 
connect  the  maxilla  strongly  with  the  frontal  bone,  which 
also  in  the  region  in  question  is  powerfully  developed  ;  the 
thick  malar  process  gives  rigidity  and  resistance  to  lateral 
movements  of  the  jaws,  and  carries  off  the  strains  to  the 
lateral  walls  of  the  cranium ;  and  the  jaw  is  buttressed  at 
the  back  by  the  pterygoid  processes. 

Taking  next  the  various  surfaces  of  the  bone,  there  are 
four,  or,  if  we  include  the  palatine  .aspect,  five  :  the  external, 
forming  a  large  part  of  the  face,  the  superior  or  orbital,  the 
internal  or  nasal,  and  the  posterior  or  zygomatic.  Upon  the 
external  or  facial  surface  we  have  to  note  the  eminence 
caused  by  the  socket  of  the  canine  tooth  (“canine  emi¬ 
nence  ”),  and  immediately  behind  this  a  depression,  the 
canine  fossa,  through  which  the  antrum  is  sometimes 
punctured.  The  alveolar  border,  from  the  situation  of  the 
third  molar  to  that  of  the  second  bicuspid,  gives  attachment 
to  the  buccinator  muscle  ;  while  immediately  beneath  the 
margin  of  the  orbit  is  the  infra-orbital  foramen,  whence 
issues  the  infra-orbital  nerve ;  hence  this  is  one  of  the 
situations  to  which  neuralgic  pain  really  dependent  on  the 
teeth  may  be  referred. 


THE  MAXILLARY  BONES. 


29 


The  orbital  and  nasal  surfaces  concern  us  only  through 
their  relation  to  the  antrum,  to  be  presently  described ;  in 
the  zygomatic  surface,  which  is  convex  and  forms  part  of 
the  zygomatic  fossa,  are  several  orifices  transmitting  the 
posterior  dental  nerves  and  vessels  ;  a  groove  which,  con¬ 
verted  by  the  apposition  of  the  palate  bone  into  a  canal, 
forms  the  posterior  palatine  canal ;  and  at  the  bottom,  a  • 
rounded  eminence,  the  maxillary  tuberosity,  which'  lies 
behind  the  wisdom  tooth,  and  has  been  occasionally  broken 
off  in  extracting  that  tooth. 

The  body  of  the  bone  is  excavated  by  an  air-chamber,  the 
antrum,  which  is  coated  in  life  by  a  continuation  of  the  nasal 
mucous  membrane,  and  this  frequently  becomes  secondarily 
involved  in  dental  disease,  so  that  its  anatomical  relations 
are  of  great  importance  to  the  dentist. 

Like  the  somewhat  similar  air  cavities  in  the  frontal  bone 
the  maxillary  sinus  does  not  attain  to  its  full  size,  relatively 
to  the  rest  of  the  bone,  until  after  the  age  of  puberty, 
although  it  makes  its  appearance  earlier  than  the  other 
nasal  sinuses,  its  presence  being  demonstrable  about  the 
fifth  month  of  foetal  life.  Hence  it  follows  that  its  walls  are 
thicker  in  the  young  subject  than  in  the  adult ;  and, 
according  to  the  observations  of  Mr.  Cattlin  (1),  it  is  some¬ 
what  larger  in  the  male  than  in  the  female. 

It  is  very  variable  in  size,  so  that  out  of  one  hundred 
adult  specimens  the  above-mentioned  writer  found  one 
which  would  only  contain  one  drachm  of  fluid,  while  in  con¬ 
trast  with  that  was  another  which  held  eight  drachms ;  two 
and  a  half  drachms  being  the  average  capacity.  Although 
it  is  exceedingly  variable  in  form  as  well  as  in  size,  it 
tends  towards  a  roughly  pyramidal  shape,  the  apex  of  the 
pyramid  being  directed  towards  the  malar  bone,  which  it 
has  been  seen  to  encroach  upon,  and  the  base  towards  the 
nasal  cavity ;  it  is,  however,  useless  to  minutely  describe 

f1)  “  Transactions  of  the  Oil  ontological  Society,”  vol.  ii.  185,7. 


30 


A  MANUAL  OF  DENTAL  ANATOMY. 


its  form,  inasmuch  as  the  two  antra  in  the  same  individual 
are  sometimes  quite  dissimilar.  The  floor  of  the  cavity  is 
rendered  uneven  in  most  specimens  by  prominences  corre¬ 
sponding  to  the  roots  of  the  molar  teeth,  which  ordinarily 
are  but  thinly  covered  by  its  bony  walls,  while  it  is  not  by 
any  means  rare  to  find  some  of  them  actually  bare. 

The  cavity  is  also  more  or  less  completely  subdivided  by 
bony  partitions  springing  from  its  walls,  as  is  well  exem¬ 
plified  in  the  accompanying  figure ;  these  partitions  are  for 
the  most  part  chin,  but  they  occasionally  attain  to  consider¬ 
able  thickness,  and  they  are  stated  to  occur  most  frequently 
at  the  anterior  or  posterior  angles  of  the  base  of  the 
pyramid. 

On  the  base  of  the  pyramid  is  the  orifice  by  which  it 
opens  into  the  middle  meatus  of  the  nose ;  this  orifice 
being  partly  closed  in  by  the  ethmoid,  palate,  and  inferior 
turbinated  bones,  and  also  by  soft  parts,  so  that  in  a  recent 

Fig.  13  p). 


subject  it  will  barely  admit  a  goosequill ;  and  it  should  be 
noted  that  this  orifice  opens  into  the  antrum  near  the  top, 
so  that  it  does  not  afford  a  ready  means  of  egress  to  fluids 
accumulated  in  the  cavity. 

Through  this  orifice  the  mucous  membrane  lining  the 

p)  Section  of  an  antrum  of  the  left  side,  divided  into  many  pouches 
by  bony  septa,  and  extending  into  the  malar  bone.  Drawn  from  a 
specimen  in  the  collection  of  Dr.  Maynard,  in  the  possession  of  the  Bal¬ 
timore  Dental  College. 


THE  MAXILLARY  BONES . 


3] 


antrum  is  continuous  with  that  of  the  nasal  fossm,  and, 
like  that,  it  is  ciliated  ;  but  it  differs  from  the  latter  in 
being  thinner  and  less  vascular. 

The  teeth  which  usually  come  into  the  closest  relation 
with  the  antrum  are  the  first  and  second  molars,  but  any  of 
the  teeth  situated  in  the  maxillary  bone  may  encroach  upon 
its  walls,  and  I  have  seen  an  abscess,  originating  at  the  apex 
of  the  fang  of  a  lateral  incisor,  pass  backwards  and  perforate 
the  antrum. 

Its  walls  have  four  aspects,  namely,  towards  the  orbit, 
the  nose,  the  zygomatic  fossa,  and  the  face,  while  its  floor  is 
formed  by  the  alveolar  border.  With  the  exception  only  of 
the  latter,  its  walls  are  very  thin  ;  and  this  exception  has 
an  important  practical  bearing  in  the  diagnosis  of  tumors  in 
this  region,  as  accumulations  of  fluid  or  morbid  growths 
really  situated  in  the  antrum  bulge  any  or  all  of  its  walls 
in  preference  to  the  alveolar  border,  whereas  tumors  spring¬ 
ing  from  the  base  of  the  sphenoid  or  elsewhere  and  encroach¬ 
ing  upon  the  antrum,  push  down  and  distort  the  alveolar 
border  as  easily  as  any  of  the  other  walls  of  the  cavity, 
inasmuch  as  the  pressure  caused  by  them  is  not  transmitted 
equally  in  all  directions,  as  is  the  case  when  the  medium 
transmitting  the  power  is  a  fluid. 

The  lower  maxilla  or  mandible  consists  of  a  bodv  and 

%J 

two  rami,  which  ascend  almost  perpendicularly  from  its 
posterior  extremity.  The  horizontal  portion  or  body  is 
curved  somewhat  in  a  parabolic  form ;  it  has  a  convex 
external  and  concave  internal  surface,  and  an  upper  (alveolar) 
and  a  lower  border.  On  the  convex  facial  surface  we  have 
to  note  the  ridge  marking  the  position  of  the  symphysis, 
and  below  this  the  mental  prominence.  Externally  to  this, 
below  the  line  of  contact  of  the  first  and  second  bicuspids 
(or  a  little  before  or  behind  this  point)  is  the  mental  fora¬ 
men,  which  constitutes  the  termination  of  the  inferior 
dental  canal.  Running  obliquely  upwards,  and  first  visible 


32 


A  MANUAL  OF  DENTAL  ANATOMY. 


at  a  point  a  little  distance  from  the  mental  prominence  is 
the  external  oblique  line,  which  becomes  merged  in  the  base 

Fig.  14  ( 1 ). 


of  the  coronoid  process.  Where  it  rises  as  high  as  the 
alveolar  border,  i.e.,  opposite  to  the  third  and  sometimes  the 
second  molar,  the  outer  alveolar  plate  is  strengthened  by  it, 
so  that  it  becomes  less  yielding  than  the  inner  plate.  The 
student  should  bear  this  fact  in  mind  when  extracting  a 
lower  wisdom  tooth. 

The  buccinator  is  attached  to  the  alveolar  border  oppo¬ 
site  to  the  molar  teeth  ;  the  platysma  myoides  to  the  outer 
side  of  the  lower  border  along  a  region  somewhat  further 
forward  :  the  masseter  over  whole  outer  face  and  border 
of  the  ascending  ramus  and  the  temporal  to  the  apex  and 
side  of  the  coronoid  process.  The  other  muscles  attached 
to  it  are  facial  muscles  of  expression. 

On  the  inner  surface  of  the  body  are  four  tubercles, 
situated  in  pairs  in  the  median  line,  about  opposite  to  the 
ends  of  the  roots  of  the  incisors,  but  somewhat  variable  both 

(l)  Lower  Maxillary  Bone.  2.  Ramus,  where  masseter  is  attached. 
3.  Symphysis.  5.  Mental  foramen.  6.  Exteimal  oblique  line.  8.  Angle 
of  jaw.  9.  Internal  oblique  line.  10.  Coronoid  process.  11.  Condyle. 
12.  Sigmoid  notch.  13.  Inferior  dental  foramen. 


THE  MAXILLARY  BONES. 


33 


in  position  and  in  size  in  different  individuals.  The  upper 
pair  of  tubercles  give  attachment  to  the  genio-hyo-glossus, 
the  lower  to  the  genio-hyoid  muscles  ;  they  are  interesting  to 
the  dental  student  not  only  as  giving  attachment  to  muscles 
concerned  in  deglutition,  but  as  affording  convenient  fixed 
points  for  measurements  of  the  relative  growth  of  parts  of 
the  jaAV.  Beneath  these  genioicl  tubercles  lie  the  slight 
depressions  Avhich  give  attachment  to  the  anterior  belly  of 
the  digastric  muscle,  while  between  the  two  points  alluded 
to  commences  the  internal  oblique  line,  Avhich  runs  ob¬ 
liquely  upwards  and  backwards,  becoming  more  pronounced 
as  it  extends  backwards,  and  terminating  at  the  inferior 
dental  foramen.  This  internal  oblique  ridge  marks  the  line 
of  growth  of  the  condyle  (see  Development  of  the  Jaws),  and 
gives  attachment  to  the  mylohyoid  muscle,  which  forms  the 
floor  of  the  mouth,  in  all  its  length.  Thus  the  bone  above 
the  ridge  belongs  strictly  to  the  mouth,  that  below  it  has 
more  relation  with  cervical  structures.  The  depression  for 
the  sublingual  gland  is  above  this  line,  consequently  this 
gland  is  visible  from  the  mouth  ;  that  for  the  submaxillary 
gland  is  beneath  it  and  further  back. 

The  inner  surface  of  the  ascending  ramus  gives  attach¬ 
ment  to  the  following  muscles  :  at  the  neck  of  the  condyle 
to  the  external  pterygoid  ;  on  the  inner  face  of  the  coro- 
noid  process,  as  far  doAvn  as  the  level  of  the  top  of  the 
crown  of  the  wisdom  tooth,  to  the  temporal ;  on  the  inner 
side  of  the  angle,  over  a  large  surface,  to  the  internal 
pterygoid. 

The  orifice  of  the  inferior  dental  canal  is  rough  and 
spinous,  giving  attachment  to  the  internal  lateral  ligament 
of  the  jaw,  Avhile  beneath  and  behind  it  is  the  groove  for 
the  mylohyoid  vessels  and  nerves ;  the  canal  runs  forward 
in  the  bone,  a  little  distance  beneath  the  ends  of  the  roots  of 
the  teeth,  and  emerges  at  the  mental  foramen,  turning  out, 
wards  at  an  angle  to  reach  it,  and  sending  onwards  small 


D 


A  MANUAL  OF  DENTAL  ANATOMY. 


31 

canals  to  the  incisors,  not  traceable  far.  It  is  nearer  to  the 
outer  than  to  the  inner  surface  of  the  jaw  in  the  latter  half 
of  its  course,  and  is  apt  to  be  very  close  to  the  ends  of  the 
roots  of  the  wisdom  teeth,  and  to  those  of  the  bicuspids. 
The  alveolar  processes  of  the  lower  jaw,  at  their  posterior 
part,  diverge  more  widely  than  those  of  the  upper  jaw,  the 
relative  antagonism  between  the  upper  and  lower  teeth 
being  preserved  in  this  region  by  the  former  having  an  in¬ 
clination  outwards,  the  latter  inwards.  The  ascending  rami 
join  the  body  at  an  angle  which  is  very  obtuse  in  the  foetus, 
nearly  a  right  angle  in  the  adult,  and  once  again  obtuse  in 
advanced  old  age  ;  the  explanation  of  this  change  will  be 
given  under,  the  head  of  the  Development  of  the  Jaw. 

The  articulation  of  the  human  lower  jaw  is  peculiar,  and 
allows  of  a  degree  of  play  unusual  in  a  joint.  The  ovoid 
condyles,  when  the  jaw  is  at  rest,  are  lodged  in  depressions, 
the  glenoid  fossce  of  the  temporal  bone,  formed  partly  by  the 
squamous  and  partly  by  the  vaginal  portions  of  the  bone. 
The  posterior  half  of  the  cavity  is  rough,  and  lodges  a  portion 
of  the  parotid  gland  :  the  anterior  is  smooth,  and  is  bounded 
in  front  bv  the  eminentia  articularis,  which  is  the  middle 
root  of  the  zygoma,  enters  into  the  formation  of  the  joint, 
and  is  coated  over  by  cartilage.  Between  the  condyle  of  the 
lower  jaw,  and  the  temporal  bone  lies  a  moveable  inter- 
articular  fibr o-cartilage,  which  is  an  irregular  bi-concave  oval 
plate,  the  edges  of  which  are  united  with  the  capsular  liga¬ 
ment,  so  that  the  joint  is  divided  into  two  cavities,  furnished 
with  separate  synovial  membranes  (unless  when,  as  some¬ 
times  is  the  case,  the  fibro-cartilage  is  perforated  in  its 

The  joint  is  described  as  having  four  ligaments  :  the 
capsular,  stylo  -  maxillary,  internal  and  external  lateral 
ligaments. 

The  capsular  ligament  is  but  feebly  pronounced,  and 
hardly  deserves  the  name  ;  the  stylo-maxillary  reaches  from 


THE  MAXILLARY  BOXES. 


35 


the  apex  of  the  styloid  process  to  the  angle  of  the  jaw  ;  the 
internal  lateral  from  the  spine  of  the  sphenoid  to  the  mar¬ 
gins  of  the  inferior  dental  foramen;  the  external  lateral, 
which  alone  is  a  ligament  strictly  proper  to  the  articulation, 
reaches  from  the  outer  side  and  tubercle  of  the  zygoma  to 
the  outer  surface  of  the  neck  of  the  condyle. 

The  form  of  the  articulating  surfaces  and  the  compara¬ 
tive  absence  of  retaining  ligaments  combine  to  allow  of  a 
variety  of  movement  unusual  in  any  other  than  a  ball  and 
socket  joint.  The  articulation  acts  as  a  simple  hinge  when 
the  jaw  is  simply  depressed,  and  this  is  the  only  motion 
possible  in  many  animals,  as  in  typical  carnivora.  When, 
however,  the  mouth'  is  opened  to  the  fullest  possible  extent 
the  condyle  leaves  the  glenoid  cavity,  slides  forward,  and 
rests  on  the  articular  eminence,  the  interarticular  ffbro- 
cartilage  being  carried  forward  with  it.  The  passage  of  the 
condyle  on  to  the  articular  eminence,  although  always 
taking  place  when  the  lower  jaw  is  excessively  depressed, 
takes  place  sometimes  with  but  little  depression  of  the  lower 
jaw,  which  then  passes  horizontally  forward;  or  it  may  take 
place  on  the  one  side  only,  giving  to  the  jaw  the  lateral 
movement  so  useful  in  mastication.  In  the  mastication  of 
food  the  various  movements  are  combined,  or  succeed  one 
another  with  great/ rapidity  ;  the  lateral  movements  are  not 
very  extensive,  the  outer  cusps  of  the  lower  teeth  of  one 
side  being  brought  to  antagonise  the  outer  cusps  of  the 
upper  teeth,  and  then  being  made  to  slide  forcibly  down  the 
sloping  surfaces  of  the  latter  till  they  return  to  their  normal 
antagonism ;  when  one  set  of  muscles  is  tired  the  same  pro¬ 
cess  is  gone  through  on  the  other  side  of  the  mouth. 

The  closure  of  the  jaw,  and  the  rotatory  and  oblique 
motions,  are  accomplished  by  four  pairs  of  very  powerful 
muscles  ;  these  are  antagonised  by  muscles  comparatively 
feeble  and  indirect  in  their  application. 

The  closure  of  the  jaws  is  effected  by  the  masseters  and 

d  2 


36 


A  MANUAL  OF  DENTAL  ANATOMY . 


the  temporals,  attached  to  the  outer  sides  of  the  jaw  ;  and 
the  external  and  internal  jDterygoids,  attached  to  its  inner 
sides. 

The  masseter,  temporal,  and  internal  pterygoid  muscles 
close  the  jaws  and  press  the  teeth  against  one  another,  and 


Fig.  15  (1). 


this  is  their  principal  action.  They  are  antagonised  by  the 
digastric,  the  mylohyoid,  and  the  geniohyoid  muscles,  which, 
aided  perhaps  by  the  platysma,  depress  the  lower  jaw  when 
the  hyoid  bone  is  fixed  by  its  own  depressor  muscles. 

The  external  pterygoid  draws  the  jawr  forward,  and  so  in 
some  measure  tends  to  open  it ;  as  the  two  muscles  do  not 
always,  or  indeed  generally,  act  together,  they  give  a  lateral 
movement  to  the  jaw.  The  superficial  portions  of  the 
masseter  and  the  internal  pterygoid  are  ordinarily  supposed, 
as  their  direction  is  slightly  backwards,  to  assist  in  drawing 
the  jaw  forwards,  but  Langer,  a  recent  investigator  of  their 
action,  attaches  very  little  importance  to  this,  and  indeed 
considers  that,  when  the  jaw  has  been  pulled  forwards  by 
the  external  pterygoid,  the  combined  action  of  the  internal 
pterygoid,  the  temporal,  and  the  masseter,  may  bring  it  back 
again. 


(b  Pterygoid  muscles.  1.  Upper,  and  2.  Lower  heads  of  external 
pterygoid  muscle.  3.  Internal  pterygoid  muscle. 


THE  MAXILLARY'  BONES. 


37 


In  ordinary  mastication  the  various  movements  are  com¬ 
bined  in  every  possible  manner. 

When  the  mouth  is  widely  open  the  condyles  play  upon 
the  articular  eminence  in  front  of  the  glenoid  cavity,  and 
the  external  pterygoid,  which  assists  in  wddely  opening  the 
mouth,  draws  not  only  the  condyle,  but  also  the  inter- 
articular  fibro-cartilage  forwards,  so  that  the  latter  still 
intervenes  between  the  condyle  and  the  articular  eminence. 
The  interarticular  cartilages  do  not,  however,  accompany 
the  jaw  in  its  extreme  movement,  but  are  believed  only 
to  pass  forwards  as  far  as  that  part  of  the  eminence  which 
is  slightly  hollowed  out.  As,  however,  in  dislocation  they 
accompany  the  condyles,  this  supposition  may  be  incorrect. 

The  position  of  repose  is  neither  complete  closure  nor 
opening  of  the  jaws  :  in  persons  with  enlarged  tonsils  the 
habitual  position  is  one  with  the  mouth  somewhat  more 
widely  open,  owing  to  the  difficulty  of  breathing  through  the 
nose  ;  a  fact  which  often  causes  an  irregularity  in  the 
disposition  of  the  teeth. 

The  axis  on  which  the  jaw  moves  is,  owing  to  the  bend 
of  the  ramus,  far  behind  the  glenoid  cavity ;  it  lies  very 
nearly  in  a  plane  formed  by  prolonging  the  plane  of  the 
masticating  surface  of  the  teeth. 

The  motions  executed  in  mastication  differ  much  according 
to  the  nature  of  the  food  ;  hence  it  happens  that  in  different 
animals  the  muscles  of  mastication  are  very  variously 
developed. 

Thus,  in  the  Herbivora,  which  move  their  jaws  greatly 
from  side  to  side,  as  anyone  may  observe  for  himself,  the 
pterygoids,  and  especially  the  external  pterygoid,  attain  to 
a  very  large  relative  size. 

On  the  other  hand,  in  the  Rodents,  which  move  their 
jaws  backward  and  forwards  in  gnawing,  the  masseter  is 
enormously  developed,  and  has  a  very  marked  general 
backward  direction. 


38 


A  MANUAL  OF  DENTAL  ANATOMY. 


Although  it  is  not  strictly  true,  the  masseter  and  temporal 
may  be  said  in  mammals  to  be  developed  in  an  inverse  ratio 
to  one  another :  when  one  is  large  the  other  is  not. 

The  masseter  is  at  a  maximum  in  Carnivora,  which  have 


Fig.  16  (*). 


little  lateral  movement  possible  to  their  jaws  ;  the  temporal 
is  also  highly  developed  in  many  of  the  class. 

In  the  great  apes,  the  temporal  becomes  enormously 
developed  only  at  the  period  of  second  dentition ;  this  fact, 
conjoined  with  its  size,  which  in  herbivora  seems  to  have  some 
relation  to  the  presence  or  absence  of  canines,  would  incline 
one  to  suppose  that  it  was  useful  in  that  rapid  closure  of  the 
mouth  appropriate  to  biting  when  animals  fight  or  seize  prey. 

The  form  of  the  glenoid  cavity  also  bears  an  intimate 
relation  to  the  dentition  of  the  animal,  and  the  nature  and 
extent  of  the  movement  of  its  jaws. 

Thus,  in  a  child  it  is  nearly  flat,  with  no  well  marked 
surrounding  elevations  ;  its  axis  is  transverse,  and  little 
rotary  motion  is  made  use  of.  In  the  adult  it  is  deeply 


(b  Condyle  of  the  lower  jaw,  and  glenoid  fossa  of  a  tiger. 


THE  MAXILLARY  BONES.  39 


sunk  :  the  axis  of  the  condyle  is  oblique,  and  rotary  move¬ 
ments  are  largely  made  use  of  in  triturating  food. 

In  the  Felidse,  it  is  strictly  transverse;  their  teeth,  adapted 
for  slicing  but  not  grinding,  would  gain  nothing  by  lateral 
motion,  which  is  rendered  quite  impossible  by  the  manner 
in  which  the  long  transverse  condyles  are  locked  into  the 
glenoid  cavity  by  strong  processes  in  front  and  behind. 
Curiously  enough  the  interarticular  cartilage  is  present,  but 
as  the  condyle  never  moves  forward,  the  cartilage  is  not 
attached  to  the  external  pterygoid  muscle. 

Tn  Herbivora  the  condyle  is  roundish,  the  ascending  ramus 
long,  the  pterygoid  muscles  large,  and  the  glenoid  cavity 
shallow;  in  the  whale,  which  of  course  does  not  masticate  at 
all,  there  is  no  interarticular  cartilage,  and  no  synovial  mem¬ 
brane  ;  the  articulation  is  reduced  to  a  mere  ligamentous 
attachment. 

The  harder  a  substance  is,  the  farther  back  between  the 
molars  it  is  placed ;  and  as  the  food  escapes  from  between 
the  teeth  it  is  constantly  being  replaced  by  the  lips,  cheeks, 
and  tongue,  the  buccinator  muscle  being  largely  concerned 
in  this  work  of  preventing  morsels  of  food  from  escaping 
from  the  teeth  during  its  mastication. 

Just  as  the  muscles  of  mastication  vary  in  their  relative 
development  in  accordance  with  the  food  to  be  dealt  with, 
so  also  do  the  salivary  glands. 

As  a  rule  herbivorous  creatures  have  large  parotid  glands; 
that  is  to  say,  those  creatures  which  deal  with  the  driest 
food  and  masticate  it  the  most  have  this  gland  largely 
developed.  For  instance  it  is  very  large  in  Ruminants  ; 
in  Herbivorous  Marsupials  it  is  larger,  in  the  carnivorous 
section  smaller,  than  the  submaxillaries.  When  an  especially 
viscid  fluid  is  required,  as,  for  example,  that  which  lubricates 
the  tongue  of  an  ant-eater,  this  is  furnished  by  exceedingly 
large  submaxillary  glands. 

The  face  is  to  a  very  great  extent  modelled  by  the  form 


40 


A  MANUAL  OF  DENTAL  ANATOMY . 


of  the  maxillary  bones,  and  these  again  are  found  to  be 
largely  influenced  by  the  dentition  of  the  animal,  so  that  it 
comes  to  be  true  to  say  that  the  face  of  an  animal  largely 
depends  upon  its  dentition.  Thus,  to  take  a  lion  as  an 
example,  the  snout  is  broad  owing  to  the  wide  separation 
between  the  canines,  which  gives  them  a  good  purchase  in 
grasping  a  living  prey ;  its  shortness  enables  them  to  be  used 
at  a  greater  mechanical  advantage  than  would  be  the  case 
were  they  further  removed  from  their  fulcrum  at  the  joint, 
and  the  breadth  of  the  face  below  the  eyes  is  conferred  by 
the  widely  spreading  zygomatic  arches,  which  are  obliged  to 
be  wide  to  give  passage  to  the  very  powerful  temporal 
muscles,  and  attachment  to  the  masseters. 

Without  going  into  further  details,  which  the  reader  can 
readily  supply  for  himself,  it  will  be  seen,  therefore,  that  the 
contour  of  the  face  is  largely  determined  by  the  dentition  in 
this  instance,  and  it  is  in  marked  contrast  with  the  long 
thin  snouts  of  the  insectivora,  whose  forceps-like  front  teeth 
as  a  rule  merely  pick  up  unresisting  prey,  or  with  the  long 
weak  snouts  of  the  horse  and  the  herbivora  generally.  The 
face  of  the  boar,  again,  is  largely  determined  by  the  great 
muscles  which  move  the  jaw,  and  by  the  bony  processes 
which  give  attachment  to  them. 

If  you  extend  the  jaws  forward  a  little,  project  the  teeth, 
and  widen  the  mouth  in  man,  you  get  a  coarse  animal  type 
of  face ;  and,  conversely,  by  a  reduction  of  the  maxillary 
region,  perhaps  eyen  below  the  limits  which  will  afford  space 
for  the  regular  disposition  of  the  teeth,  you  get  a  refined 
oval  type  of  face.  The  jaws  of  a  negro  are  large  relatively 
to  the  cranium,  as  are  also  those  of  exceptionally  big  men, 
such  as  we  call  giants,  though  this  is  not  universally  true  ; 
in  rickets  the  reverse  is  the  case. 

The  nerves  of  the  teeth  are  derived  from  branches  of  the 
fifth  nerve,  the  nerve  of  sensation  of  the  whole  side  of  the 
face  and  head  :  the  lower  teeth  through  the  inferior  maxil- 


Fig.  17  (]). 


(l)  Diagram  of  the  Distribution  of  the  Branches  of  the  Fifth  Nerve. 

(From  Tomes’  “Lectures  on  Dental  Physiology  and  Surgery  ” — drawn  by  Mr.  C.  De  Morgan.) 

A.  Ophthalmic  division  : — 1.  Frontal.  2.  Nasal  and  long  ciliary.'  3.  Branches  to  ciliary  ganglion. 

B.  Superior  maxillary  division  4.  Orbital  J  J  5'.  Sphenopalatine  (Meckel’s)  ganglion. 

6.  Posterior  dental,  passing  down.  7,  8.  Anterior  dental.  9.  Infra-orbital. 

C.  Inferior  maxillary  division:— 10.  Auriculo-temporal.  11.  Masseteric.  12.  Deep  temporal.  13.  Ptery¬ 

goid.  14.  Buccal  to  buccinator,  &c.  15.  Gustatory.  16.  Mylohyoid  branch.  17.  Inferior  dental 

18.  Mental. 


[To  face  p.  40. 


\ 


DR  H.  WALTER 


/ 


/ 


THE  MAXILLARY  BONES. 


41 


lary  nerve,  the  upper  through  the  anterior  and  posterior 
dental  branches  of  the  superior  maxillary  nerve.  The  nerves 
are  given  off  from  the  nerve  trunks  in  bundles  corresponding 
in  number  to  the  roots  of  the  teeth  for  which  they  are  des¬ 
tined.  For  the  details  of  the  distribution  of  the  fifth  nerve 
the  student  must  refer  to  works  treating  of  anatomy,  as  it 
would  be  out  of  place  to  enter  upon  the  subject  at  length  in 
these  pages,  in  which  merely  one  or  two  matters  of  special 
interest  to  the  dental  student  will  be  touched  upon. 

In  the  case  of  the  inferior  maxillary  nerve  the  roots  of 
the  teeth  come  into  very  close  proximity  with  the  main 
trunk  of  the  nerve  ;  this  is  especially  the  case  with  the 
lower  wisdom  teeth.  Within  a  few  days  of  writing  these 
lines  I  extracted  a  lower  wisdom  tooth  (with  forceps)  for  a 
gentleman,  who,  immediately  after  the  extraction,  inquired 
if  he  could  have  bitten  his  lip,  as  it  felt  swollen ;  on 
testing  it  I  found  slight  but  well  marked  numbness  on  that 
side  of  the  lip  and  chin,  which  did  not  wholly  subside  before 
he  left  me.  In  this  case  a  groove  upon  the  under  surface  of 
the  much  curved  roots  appeared  to  indicate  that  the  nerve 
trunk  was  in  close  contact  with  the  tooth. 

No  reason  is  at  present  known  why  the  tooth  pulp  should 
be  so  richly  supplied  with  nerves,  unless  it  confers  greater 
tactile  sensibility  upon  the  whole  tooth.  Teeth  with  per¬ 
sistent  pulps  which  go  on  growing  throughout  the  life  of 
the  animal,  have  always  large  nerves :  thus  a  very  large 
trunk  goes  to  the  pulp  of  a  rodent  incisor.  But  although  in 
this  case  the  rich  nervous  supply  doubtless  has  to  do  with 
nutrition,  and  presides  over  the  great  formative  activity  of 
the  tissue,  this  does  not  fully  account  for  the  pulps  of  the 
teeth  of  limited  growth  being  so  amply  supplied  with  nerves. 

As  has  been  mentioned  in  the  description  of  the  lower 
maxillary  bone,  the  inferior  dental  nerve  emerges  from  the 
bone  by  the  mental  foramen,  near  to  the  end  of  the  roots  of 
the  bicuspid  teeth.  Pain  due  to  distant  causes  is  often 


42 


A  MANUAL  OF  DENTAL  ANATOMY. 


referred  to  the  point  of  emergence  of  a  nerve,  as  is  so 
frequently  exemplified  in  supraorbital  neuralgia;  in  the 
same  way  pain  due  to  diseased  teeth  far  back  in  the  lower 
jaw  (especially  to  wisdom  teeth),  is  frequently  referred  to 
the  bicuspid  region.  Curiously  enough,  though  there  is  no 
apparent  close  parallel  in  the  disposition  of  the  nerves,  a 
similar  reference  of  pain  to  the  bicuspid  region  is  occasionally 
observed  in  the  upper  jaw.  And  it  may  be  added  that  there 
is  very  probably  some  closer  parallel  in  the  minute  disposi¬ 
tion  of  the  nerve  fibres  going  to  the  teeth  in  the  upper  and 
lower  jaws  than  is  recognisable  by  rough  anatomical  pro¬ 
cesses,  for  while,  to  all  appearance,  the  nerve  trunks  are 
differently  arranged,  it  is  a  matter  of  almost  everyday  ob¬ 
servation  to  find  pain  due  to  one  tooth  referred  with  pre¬ 
cision  to  its  fellow  in  the  other  jaw. 

The  lower  teeth  derive  their  vascular  supply  from  the 
branches  given  off  to  each  tooth  by  the  inferior  dental  artery, 
itself  a  branch  of  the  internal  maxillary ;  the  upper  teeth 
derive  their  arteries  from  the  superior  dental,  a  part  of  the 
alveolar  branch  of  the  internal  maxillary,  which  supplies 
the  molar  and  bicuspid  teeth ;  and  the  front  teeth  from  the 
descending  branch  of  the  infraorbital,  the  vessels  thus  having 
an  arrangement  somewhat  analogous  to  that  of  the  nerves. 

The  distribution  of  the  veins  corresponds  closely  to  that  of 
the  arteries. 

No  lymphatics  have  been  traced  into  the  teeth,  though 
lymph  spaces  are  described  by  Dr.  Black  as  existing  in  the 
alveo  ar  dental  periosteum. 


Tomes,  J.  Lectures  on  Dental  Physiology  and  Surgery.  1848. 
Harrison  Allen.  Anatomy  of  the  Facial  Region,  Dental  Cosmos. 

1874. 

Cattlin.  Anatomy  of  Antrum.  Trans.  Odontological  Society. 
1857. 

Black.  Periosteum  and  Peridental  Membrane.  Chicago,  1887. 


i 


CHAPTER  III. 


THE  DENTAL  TISSUES. 

It  is  usual  to  speak  of  there  being  two  kinds  of  teeth, 
namely,  horny  or  albuminous,  and  calcified  teeth  ;  but  the 
development  of  the  former  is  nob  yet  fully  known,  and  it  is 
lienee  impossible  to  determine  the  exact  relation  in  which 
they  really  stand  to  other,  or  calcified,  teeth. 

The  horny  teeth  of  Ornithorhyncus  have  been  shown 
to  be  purely  epithelial,  and  to  consist  entirely  of  cells  of 
the  stratum  corneum  arranged  in  parallel  columns  which 
are  penetrated  by  papillary  processes  of  the  oral  epi¬ 
thelium.  In  other  words  they  are  an  aggregation  of  long 
papillae,  in  which  the  stratum  corneum  is  abundant  and  hard, 
squeezed  together  to  form  a  coherent  mass.  These  horny 
teeth  do  the  work  of  mastication  during  the  greater  part  of 
the  animal’s  life,  but  when  the  creature  was  half  grown,  it 
possessed  true  teeth  with  multi-cuspid  grinding  surfaces  and 
short  stunted  roots.  At  that  period  the  horny  plates  were 
not  fully  formed,  but  they  were  situated  underneath  the 
true  teeth,  and  were  incomplete  only  where  the  roots  of  the 
teeth  passed  through  them.  When  the  teeth  were  shed 
they  became  complete,  but  the  peculiar  sculpturing  of  their 
surfaces  is  due  to  their  having  once  formed  a  bed  for  the 
short- rooted  molars.  But  they  are  obviously  not  in  any 
way  homologous  with  true  teeth.  The  horny  teeth  which 
surround  the  sucking  mouth  of  the  lamprey  are  found 
to  consist  of  one  or  more  superimposed  horny  cones, 


44 


A  MANUAL  OF  DENTAL  ANATOMY. 


standing  upon  a  dermal  papilla,  and  arising  from  a  horn- 
producing  groove  around  the  base  of  the  papilla  (Beard, 
Morphological  Studies,  Jena,  1889).  But  the  horny  tooth  of 
Myxine  (the  Hag)  is  yet  more  remarkable  :  in  it  the  horny 
cone  is  superimposed,  not  upon  a  simple  papilla,  but  upon  a 
tooth  germ  which  goes  on  to  a  considerable  degree  of  calci¬ 
fication.  Like  the  horny  cones  of  the  lamprey,  its  free  edges 
rest  in  a  horn-forming  groove  of  oral  epithelium.  Inside  this 
is  a  hard  cone  which  appears  to  be  a  form  of  imperfect 

Fig.  18  (*). 


he 


dentine  (with  vascular  canals  in  it  ? ) :  this  Prof.  Beard 
believes  to  be  capped  with  enamel  in  one  of  his  specimens, 
and  in  the  interior  of  this  is  a  .pulp  with  odontoblasts. 
There  is  great  difficulty  in  making  out  the  structure,  as 
these  combined  horny  and  calcified  teeth  almost  defy  ordinary 
methods  of  preparation. 

The  figure  given  above  is  somewhat  diagrammatic,  and  is 

O  Tooth  of  Myxine.  d.  Dentine  cap.  e.  Enamel  (?).  h,  e.  Horn  form¬ 
ing  epithelium,  p.  Pulp. 


THE  DENTAL  TISSUES. 


45 


compounded  from  Dr.  Beard’s  figures,  and  from  a  section 
which  he  was  so  kind  as  to  lend  me. 

Between  the  horny  cap  and  the  dentine  is  an  epithelial 
structure  which  is  in  the  position  of,  and  seems  to  play  the 
part  of,  an  enamel  organ. 

Calcified  teeth  are  composed  of  one  or  more  structures, 
which  are  in  great  measure  peculiar  to  the  teeth  (although, 
what  is  to  all  intents  and  purposes  dentine,  is  to  be  found 
in  the  skeletons  and  in  the  dermal  appendages  of  some  fish, 
and  other  exceptions  might  be  found  to  the  absolute  accu¬ 
racy  of  the  statement),  and  hence  are  called  “dental  tissues.” 
Notwithstanding  the  existence  of  certain  transitional  forms, 
it  is  not  possible  to  doubt  the  propriety  of  a  general  division 
of  dental  tissues  into  three  viz.,  Dentine,  Enamel,  and 
Cementum. 

The  first  named  of  these  constitutes  the  greater  part  of 
all  teeth,  and  so  far  predominates  in  mass  over  the  other 
constituents  that,  in  very  many  cases,  the  tooth  would 
retain  its  form  and  character  after  the  removal  of  the  enamel 
and  cementum. 

This  central  body  of  dentine,  enclosing  the  pulp,  is  very 
often  covered  by  a  cap  of  enamel,  which  forms  the  surface 
of  the  tooth  ;  this  may  be  very  partial,  as  in  the  eel  or  the 
newt,  in  which  animals  only  this  enamel- capped  tip  of  the 
tooth  ju’ojects  far  above  the  surface  of  the  mucous  membrane ; 
or  it  may  cover  a  much  larger  proportion  of  the  tooth,  as 
in  man.  Perhaps  the  most  usual  condition  is  that  the 
enamel  invests  the  whole  crown  of  the  tooth,  stopping  short 
at  about  the  level  to  which  the  gum  reaches,  as  in  the 
human  and  most  other  mammalian  teeth  of  limited  growth. 
In  teeth  of  persistent  growth  the  enamel  extends  down  into 
the  socket  as  far  as  the  base  of  the  tooth  ;  in  such  cases  it 
may  embrace  the  whole  circumference  of  the  dentine,  as  in 
the  molar  teeth  of  many  rodents,  or  it  may  be  confined  to 
one  side  only,  as  in  their  incisor  teeth,  where  by  its  greater 


46 


A  MANUAL  OF  DENTAL  ANATOMY. 


hardness  it  serves  to  constantly  preserve  a  sharp  edge  as 
the  tooth  is  worn  away.  The  enamel  is  believed  to  be  quite 
absent  from  many  teeth ;  thus  the  subclass  Edentata  com¬ 
prising  sloths,  armadillos,  and  ant-eaters  have  it  not ;  the 
narwal,  certain  cetaceans,  some  reptiles,  and  many  fish  have 
none. 

But  although  it  might  appear  an  exceedingly  simple 
matter  to  determine  whether  a  tooth  is  or  is  not  coated  with 
enamel,  as  a  matter  of  fact  in  practice  it  is  not  always  easy 
to  be  certain  upon  this  point.  When  the  enamel  is  tolerably 
thick  there  is  no  difficulty  in  making  sections  which  show 
it  satisfactorily,  but  when  it  is  very  thin  it  is  apt  to 
break  off  in  grinding  down  the  section.  And  even  when  it 
does  not,  it  is  in  such  cases  usually  quite  transparent  and 
structureless,  and  the  outermost  layer  of  the  dentine  being 
also  clear  and  structureless,  it  is  very  hard  to  decide  whether 
the  appearance  of  a  double  boundary  line  is  a  mere  optical 
effect  due  to  the  thickness  of  the  section,  or  is  indicative  of 
a  thin  layer  of  a  distinct  tissue  which  might  be  either 
enamel  or  cementum. 

My  own  investigations  upon  the  development  of  the  teeth 
of  fish  and  reptiles  have  led  me  to  suspect  that  rudimentary 
layers  of  enamel  exist  upon  many  teeth  on  which  their 
presence  has  not  been  recognised,  for  I  have  found  that  the 
formative  enamel  organs  occur  universally,  at  least  they 
exist  upon  all  tooth  germs  which  have  been  adequately  ex¬ 
amined.  Upon  the  teeth  of  snakes,  which  were  stated  by 
Professor  Owen  to  be  composed  only  of  dentine  and  cement, 

I  have  endeavoured  to  show  that  a  thin  layer  of  enamel 
exists,  and  that  there  is  no  cementum.  The  frog  has  an 
enamel  organ  as  distinct  as  that  of  the  snake,  but  I  am 
hardly  positive  that  there  is  enamel  upon  its  teeth,  although 
there  is  an  appearance  of  a  thin  coat  of  distinct  tissue.  I 
have  also  demonstrated  that  the  armadillo  has  an  enamel 
organ,  but  have  failed  to  discover  any  enamel  or  anything 


THE  DENTAL  TISSUES. 


47 


like  it  upon  its  teeth,  and  Professor  Sir  Win.  Turner  has 
made  a  similar  observation  upon  the  narwal. 

At  all  events  we  may  safely  say  that  in  these  and  many 
other  creatures  no  functional  development  of  enamel  takes 
place  :  whether  it  does  or  does  not  exist  in  an  extremely 
thin  and  rudimentary  layer  has  become  a  question  of  much 
less  significance,  since  I  have  shown  the  presence  of  an 
enamel  organ  to  be  probably  universal  at  an  early 
stage. 

Hence  I  feel,  some  hesitation  in  endorsing  Professor  Owen’s 
generalisation  that  the  dentine  is  the  most  and  enamel  the 
least  constant  of  dental  tissues  ;  it  is  possible  that  it  may  be 
so,  but  recent  researches  into  the  development  of  teeth  have 
very  materially  modified  the  conceptions  formed  as  to  the 
relations  of  the  dental  tissues  to  one  another,  and  must  lead 
us  to  examine  carefully  into  such  deductive  statements 
before  accepting  them. 

The  remaining  dental  tissue  is  cementum,  which  clothes, 
in  a  layer  of  appreciable  thickness,  the  roots  of  the  teeth, 
and  reaches  up  as  far  as  the  enamel,  the  edge  of  which  it 
overlaps  to  a  slight  extent ;  when  the  cementum  is  present 
upon  the  crown,  it  occupies  a  position  external  to  that  of 
the  enamel.  Cementum  occurs  universally  upon  the  teeth 
of  mammalia,  but  it  is  not  always  confined  to  the  root  of 
the  tooth  ;  in  many  teeth  of  persistent  growth  it  originally 
invested  the  whole  crown,  and  after  it  has  been  worn  from 
the  exposed  grinding  surface,  continues  to  invest  the  sides 
of  the  tooth.  (See  the  description  of  the  complex  teeth  of 
the  elephant,  cow,  horse,  &c.) 

It  is  probably  entirely  absent  from  the  teeth  of  snakes,  and 
indeed  of  very  many  reptiles  ;  in  the  reptilian  class,  at  all 
events,  it  appears  to  me  to  be  confined  to  those  in  which  the 
teeth  are  lodged  either  in  sockets  or  in  a  deep  bony  groove, 
as  I  am  unacquainted  with  any  tooth  anchylosed  to  the  jaw 
in  which  it  exists,  unless  we  are  inclined  to  include  under  the 


48 


A  MANUAL  OF  DENTAL  ANATOMY 


term  cementum  the  tissue  which  I  have  designated  “  bone 
of  attachment.”  (See  “  Implantation  of  Teeth.”) 


ENAMEL. 

Upon  the  outer  surface  of  the  dentine  the  enamel  forms 
a  cap  of  a  very  much  harder  and  denser  material.  In 
its  most  perfect  forms  it  is  very  far  the  hardest  of  all 
tissues  met  with  in  the  animal  body,  and  at  the  same 
time  the  poorest  in  organic  matter.  In  the  enamel  of  a 
human  adult  tooth  there  is  as  little  as  3 4  *to  5  per  cent, 
of  organic  matter,  and,  judging  from  its  brittleness  and 
transparency,  there  is  probably  even  less  in  the  enamel 
of  some  lower  animals  ;  the  lime  salts  consist  of  a  large 
quantity  of  calcium  phosphate,  some  carbonate,  and  a  trace 
of  fluoride ;  in  addition,  there  is  a  little  magnesium 
phosphate. 

Von  Bibra  gives  two  analyses  of  enamel : 


Calcium  Phosphate  and  Fluoride  . 

ADULT 

MAN. 

89*82 

ADULT 

WOMAN. 

81-63 

Calcium  Carbonate  .  .  .  . 

4-37 

8-88 

Magnesium  Phosphate 

1-34 

2-55 

Other  Salts  .  .  .  .  . 

GO 

00 

•97 

Cartilage  ..... 

3-39 

5-97 

Fat.  .  .  .  .  .  . 

•20 

a  trace 

Organic  .  .  .  . 

3-59 

5-97 

Inorganic  .  .  .  .  . 

96-41 

94-03 

Owing  to  the  very  small  proportion  of  organic  matter 
enamel  when  treated  with  a  mineral  acid  wholly  disappears, 
no  organic  framework  being  left  behind.  The  structure  of 
enamel,  composed  as  it  is  of  prisms  of  calcified  material,  is 
closely  imitated  in  the  invertebrate  world  by  the  shell  of 
Pinna  and  many  other  molluscs,  but  these  differ  in  several 


THE  DENTAL  TISSUES. 


49 


respects,  amongst  others  in  having  so  large  a  proportion  of 
organic  basis  as  to  retain  a  structure  after  decalcification. 
The  cap  of  human  enamel  is  of  varying  thickness,  being 
thicker  in  the  neighbourhood  of  cusps  than  elsewhere  ;  in 
teeth  of  limited  growth  it  terminates  by  a  thin  edge  at  the 
neck  of  the  tooth,  where  it  is  overlapped  to  some  slight 
extent  by  the  cementum.  When  a  thick  coating  of  cemen- 
turn  exists  over  the  whole  crown,  this  lies  outside  the 
enamel,  the  proper  place  of  which  is  therefore  between  the 
cementum  and  the  dentine. 

The  external  surface  of  human  enamel  is  finely  striated, 
the  course  of  the  striae  being  transverse  to  the  long  axis  of 
the  crown  ;  in  addition  to  this  very  fine  striation,  there  may 
be  a  few  deeper  and  more  pronounced  grooves  or  pits,  which 
are  pathological,  and  are  marks  of  checks  in  development 
more  or  less  complete.  The  enamel  of  some  animals  is,  to 
all  appearance,  structureless  ;  such  is  the  nature  of  the 
little  caps  which,  like  spear  points,  surmount  the  teeth  of 
fishes  of  the  eel  tribe,  cod  tribe,  or  of  the  newt,  and  which 
from  their  extreme  brittleness  are  often  lost  in  preparing 
sections,  so  that  their  very  existence  has  long  been  over¬ 
looked.  But  the  absence  of  structure,  if  such  it  really  be,  is 
after  all  a  mere  question  of  degree  ;  in  the  commonest  form 
of  enamel,  such  as  that  of  the  human  teeth,  there  is  a  finely 
fibrous  structure,  very  apparent  in  imperfect  teeth,  but  far 
less  so  in  well-formed  ones,  and  the  enamel  of  the  eel  is,  in 
the  manner  of  its  development,  fibrous  ;  so  that  even  though 
we  cannot  distinguish  its  constituent  fibres  when  it  is  com¬ 
pleted,  this  is  merely  an  indication  that  calcification  has 
progressed  a  little  farther  than  in  human  teeth  :  if  calcifica¬ 
tion  only  goes  far  enough,  all  structure,  if  not  destroyed, 
will  at  all  events  be  masked  from  sight. 

The  structure  of  human  enamel  has  been  stated  to  be 
fibrous  ;  that  is  to  say,  it  has  a  cleavage  in  a  definite  direc¬ 
tion,  and  is  capable  of  being  broken  up  into  fibres  or  prisms 


E 


50 


A  MANUAL  OF  DENTAL  ANATOMY . 


which  seem  in  transverse  section  to  approximate  more  or 
less  closely  to  hexagonal  forms  brought  about  by  their 
mutual  apposition.  The  prisms  run  from  the  dentine  towards 
the  free  surface ;  this  is,  ^however,  subject  to  many  minor 
modifications.  The  curved  and  decussating  course  of  the 
human  enamel  prisms  renders  it  difficult  to  trace  them 
throughout  their  length,  but  the  structure  of  the  enamel  of 
many  lower  animals  (especially  the  rodents)  is  more  easily 
intelligible.  Enamel  such  as  that  of  the  Manatee,  in  which 
all  the  prisms  pursue  a  perfectly  straight  course,  is  of  com¬ 
paratively  rare  occurrence ;  but  among  the  rodents  the  courses 
pursued  by  the  enamel  prisms  are  simple,  and  produce  very 
regular  patterns,  which  are  constant  for  particular  families 
(J.  Tomes).  Thus,  in  the  Sciurid&e,  a  section  of  the  enamel, 
whether  longitudinal  or  transverse,  appears  divided  into 
an  outer  and  inner  portion,  in  which  the  prisms,  although 
continuous  from  the  dentine  to  the  free  surface,  pursue 
different  directions.  As  seen  in  longitudinal  section,  the 
enamel  prisms  start  from  the  dentine  at  right  angles  to  its 
surface,  and  after  passing  through  about  two-thirds  of  the 
thickness  of  the  enamel  in  this  direction,  abruptly  bend  up¬ 
wards,  forming  an  angle  of  45  degrees  with  their  original 
course.  In  transverse  section  the  enamel  prisms  are  found 
to  be  arranged  in  horizontal  layers,  each  layer  being  a  single 
fibre  in  thickness ;  in  alternate  layers  the  prisms  pass  to  the 
right  and  to  the  left,  crossing  those  of  the  next  layer  at  right 
angles,  and  thus  making  a  pattern  of  squares  in  the  inner  two- 
thirds  of  the  enamel.  But  in  the  outer  third  of  the  enamel, 
where  the  prisms  bend  abruptly  upwards,  those  of  superim¬ 
posed  layers  no  longer  pass  in  opposite  directions,  but  are  all 
parallel ;  in  fact  no  longer  admit  of  distinction  into  lamina). 

Thus  each  enamel  prism  passes  in  a  very  definite  direction, 
and,  seen  with  those  of  other  layers,  forms  a  very  charac¬ 
teristic  pattern ;  but  the  enamel  prisms  are  not  in  any  part 
of  their  course  curved. 


THE  DENTAL  TISSUES. 


51 


In  the  beaver,  from  which  the  following  figure  is  taken, 
the  arrangement  of  the  enamel  prisms  is  dissimilar  in  the 
upper  and  lower  teeth,  the  lamination  taking  place  in 
different  directions,  so  that  a  longitudinal  section  of  the  one 
might,  so  far  as  this  is  concerned,  be  mistaken  for  a  trans¬ 
verse  section  of  the  other.  As  regards  the  decussation  of 


Fig.  19  (l). 


the  prisms  of  alternate  layers,  it  is  similar  to  that  of  the 
SciuridEe,  but  it  differs  in  the  laminae  being  slightly  flexuous 
instead  of  pursuing  perfectly  straight  lines. 

In  the  porcupine  family  very  much  more  complex 
patterns  are  met  with,  the  enamel  prisms  being  individually 
flexuous,  and  their  curves  not  being  confined  to  one  plane  ; 
the  individual  prisms  pursue  a  serpentine  course,  and  cannot 
be  followed  far  in  any  one  section.  Near  to  the  surface, 
however,  they  all  become  parallel,  the  enamel  thus  conform¬ 
ing  with  that  of  other  rodents  in  being  divided  into  two 
portions  (at  least  so  far  as  the  course  pursued  by,  and 
the  pattern  traced  by,  its  fibres  in  its  inner  and  outer 
parts  can  be  said  to  so  divide  it).  The  Leporidse,  or  hares, 
form  an  exception ;  their  enamel  has  no  such  lamelliform 

(b  Section  of  dentine  and  enamel  of  a  Beaver  :  in  the  inner  half  the 
prisms  of  contiguous  layers  cross  each  other  at  right  angles,  in  the  outer 
they  are  parallel. 

E  2 


DR.  a  VtALTBh 


52 


A  MANUAL  OF  DENTAL  ANATOMY. 


arrangement,  but  is  built  up  merely  of  slightly  flex  nous 
prisms. 

By  tracing  the  courses  of  enamel  prisms  from  the  simple 
pattern  found  in  the  Manatee  through  that  of  the  squirrel, 
dormouse,  and  the  porcupine,  we  see  how  a  very  definite 
arrangement,  at  first  simple,  becomes  modified  into  some¬ 
thing  a  little  more  complex,  till  at  last  it  reaches  a  degree 
of  complexity  that  looks  like  mere  disorder.  No  one  un¬ 
familiar  with  the  enamel  of  other  rodents,  looking  at  the 


Fig.  20  (x). 


enamel  of  the  porcupine,  would  be  able  to  unravel  the  very 
indefinite  looking  chaos  of  prisms  before  him  ;  but  had  he 
studied  forms  in  some  degree  transitional  he  could  not  doubt 
that  the  tortuous,  curving  course  which  he  saw  the  prism 
to  be  pursuing  was  nevertheless  perfectly  definite  and  precise, 
and  formed  part  of  a  regular  pattern. 

In  perfectly  healthy  human  enamel  the  fibrillar  arrange¬ 
ment  is  not  so  very  strongly  marked  the  prisms  are  solid, 
are  apparently  in  absolute  contact  with  one  another,  without 
visible  intervening  substance. 

But  Bodecker,  basing  his  conclusions  upon  the  examination 

(])  Human  enamel,  from  tlie  masticating  surface  of  a  molar.  The 
figure  is  merely  intended  to  show  the  general  direction  of  the  fibres. 


THE  DENTAL  TISSUES. 


53 


of  thin  sections  stained  with  chloride  of  gold,  holds  that 
enamel  is  built  up  of  columns  of  calcified  substance,  between 
which  minute  spaces  exist.  These  are  filled  by  a  material 
which  takes  the  stain  deeply,  and  is  probably  analogous  to 
the  cement  substance  of  epithelial  formations.  As  seen  in 
sections,  it  gives  off  exceeding  fine  thorns,  which  apparently 
j)ierce  the  prisms  at  right  angles  to  their  length,  so  that  it 
forms  a  close  network  very  intimately  mixed  up  with  the 
calcified  portion  of  the  enamel. 

It  is  not  of  uniform  thickness,  but  is  beaded,  and  Bodecker 
attributes  it  to  a  role  of  far  greater  importance  than  that  of 
a  mere  cementing  substance,  for  he  regards  it  as  being  an 
active,  protoplasmic  network,  which  renders  the  enamel 
much  more  “  alive  ”  than  it  has  hitherto  been  considered  to 
be.  He  believes  it  to  become  continuous  with  the  soft 
contents  of  the  dentinal  tubes  through  the  medium  of  large 
masses  of  protoplasmic  matter  found  at  the  margins  of  the 
enamel  and  dentine. 

But  although  there  are  various  reasons  for  suspecting  that 
enamel  is  not  completely  out  of  the  pale  of  nutrition  from 
the  moment  that  a  tooth  is  cut,  yet  further  observations  are 
needed  before  the  activity  and  importance  of  the  cement 
substance  demonstrated  by  Bodecker  can  be  held  to  be  fully 
established.  Klein  remarks  that  u  the  enamel  cells,  like  all 
epithelial  cells,  being  separated  from  one  another  by  a  homo¬ 
geneous  interstitial  substance,  it  is  clear  that  the  remains 
of  this  substance  must  occur  also  between  the  enamel 
prisms ;  in  the  enamel  of  a  developing  tooth  the  interstitial 
substance  is  larger  in  amount  than  in  the  fully  formed 
organ.  It  is  improbable  that  nucleated  protoplasmic  masses 
are  contained  in  the  insterstitial  substance  of  the  enamel 
of  a  fully-formed  tooth,  as  is  maintained  quite  recently  by 
Bodecker.” 

The  study  of  the  development  of  marsupial  enamel,  to  be 
alluded  to  at  a  future  page,  by  showing  that  the  enamel  is 


54 


A  MANUAL  OF  DENTAL  ANATOMY. 


penetrated  by  soft  tissue  differently  placed,  also  tends  to 
throw  doubt  upon  Bodecker’s  interpretation.  W.  J.  Bark  as 
( Monthly  Review  of  Dental  Surgery,  1874)  has  perhaps 
had  this  cementing  substance  under  observation  ;  he  also 
believes  that  the  enamel  prisms  of  human  enamel  are  tubular, 
minute  canals  running  along  their  axes. 

On  the  whole  the  prisms  are  parallel,  and  run  from  the 
surface  of  the  dentine  continuously  to  that  of  the  enamel. 
Their  paths  are  not,  however,  either  perfectly  straight  or 
perfectly  parallel,  for  alternate  layers  appear  to  be  inclined 
in  opposite  directions,  while  they  are  also  wavy,  forming 
several  curves  in  their  length.  The  curvature  of  the  enamel 
prisms  is  most  marked  upon  the  masticating  surface ;  while 
the  layers,  alternating  in  the  direction  of  their  inclination 
as  just  described,  are  in  planes  transverse  to  the  long  axis 
of  the  crown,  and  correspond  to  the  fine  striae  on  the  surface 
of  the  enamel,  which  appear  to  be  caused  by  their  outcrop. 
The  curvatures  take  place  in  more  than  one  plane  ;  in  other 
words,  the  course  of  the  individual  prism  is  more  or  less  of 
a  spiral. 

Although  most  prisms  run  through  the  whole  thickness 
of  the  enamel,  yet  inasmuch  as  the  area  of  the  outer  is  much 
larger  than  that  of  the  inner  surface  of  the  enamel,  and  the 
individual  prisms  do  not  undergo  any  alteration  in  size  as 
they  pass  outwards,  many  supplemental  fibres  are  present  in 
the  outer  portions  of  the  enamel  which  do  not  penetrate  far 
inwards. 

The  individual  fibres  are  to  all  appearance  structureless 
in  perfectly  formed  human  enamel,  but  a  faint  transverse 
striation,  fainter,  but  otherwise  not  unlike  that  of  voluntary 
muscle,  is  so  general  that  it  cannot  be  regarded  as  patho¬ 
logical,  although  it  is  most  strongly  developed  in  imperfect 
brownish  enamel.  The  striation  in  question  may  be  seen 
even  in  a  single  isolated  fibre,  and  is  not  necessarily  con¬ 
tinuous  over  adjacent  fibres,  though  it  often  is  so  j  it  is 


THE  DENTAL  TISSUES. 


55 


rendered  more  apparent  by  the  slight  action  of  diluted  acids 
upon  the  fibre.  Very  various  interpretations  of  this  appear¬ 
ance  have  been  given.  It  has  been  attributed  to  “an  inter¬ 
mittent  calcification  ”  of  the  enamel  fibre  (Hertz),  but  is 
with  more  probability  referred  to  varicosities  in  the  indi¬ 
vidual  fibres  (Kolliker,  Waldeyer)  (1).  It  is  very  marked  in 
the  enamel  of  the  common  rat,  which  shares  with  that  of 
other  muridte  the  peculiarity  of  having  the  individual  fibres 
almost  serrated,  those  of  adjacent  crossing  layers  being  fitted 
to  one  another  with  great  exactness.  In  human  enamel  the 
adjacent  fibres,  if  united  without  any  intermediate  cement¬ 
ing  medium,  and  pursuing  courses  slightly  different,  must 
of  necessity  be  of  slightly  irregular  form,  or  else  interspaces 
would  be  left,  which  is  not  found  to  be  the  case.  Thus  the 
“decussation  of  the  fibres”  is  a  plausible  explanation  of  this 
appearance  of  striation  ;  indeed  isolated  fibres  do  present  an 
appearance  of  slight  varicosities,  repeated  at  regular  in¬ 
tervals.  That  the  striation  of  enamel  prisms  is  due  to  this 
cause  is  confirmed  by  Mr.  Febiger,  an  American  expert 
in  the  resolution  of  diatoms,  to  whom  enamel  sections 
were  submitted  for  his  opinion  by  Dr.  Xavier  Sudduth. 
The  penetration,  at  regular  intervals,  of  the  prisms  by  the 
“  thorns  ”  of  cement  substance  (see  page  53),  affords  another 
possible  explanation. 

Although  the  perfect  enamel  fibre  appears  to  be  entirely 
homogeneous,  it  is  not  really  so,  for  acids  act  with  far  greater 
rapidity  upon  the  central  or  axial  portion  of  the  fibre  than 
upon  its  periphery.  The  accompanying  figure,  taken  from 
enamel  softened  by  maceration  in  a  J  per  cent,  solution 
of  chromic  acid,  shows  this  well ;  the  central  portions  of 
the  fibre  are  dark,  and  are  stained  green  by  the  reduced 
chromium  sesquioxide,  while  the  clear  interspaces  are 

(])  The  striation  of  voluntary  muscle  has  been  alleged  to  be  due 
to  this  same  cause  (Dr.  Haycraft,  “Proceedings  of  Royal  Society,”  Feb. 
1881). 


56 


A  MANUAL  OF  DENTAL  ANATOMY. 


colourless.  Again,  if  dilute  hydrochloric  acid  be  applied  to 
a  section  of  enamel,  the  axial  part  of  the  fibres  are  first 
attacked  and  are  dissolved  away,  so  that,  if  the  section  be 
transverse,  a  fenestrated  mass  remains.  During  the  forma- 

Fig.  21  p). 


tion  of  enamel  the  hardening  salts  are  deposited  first  in  the 
periphery  of  the  enamel  cells,  so  that  the  youngest  layer  of 
enamel  is  full  of  holes,  each  one  of  which  corresponds  to  the 
centre  of  a  fibre.  Although  calcification  goes  on  to  obliterate 

Fig.  22  (2). 


the  visible  difference  between  the  centre  and  the  periphery 
of  the  enamel  fibre,  yet  the  action  of  an  acid  reverses  the 
order  of  its  formation  and  once  more  makes  it  fenestrated, 
indicating  that  there  is  not  absolute  identity  of  substance 
in  the  inner  part  of  the  fibre.  In  imperfect  enamel,  indeed, 

(1)  From  human  enamel,  softened  in  chromic  acid,  until  it  could  he 
readily  cut  with  a  knife. 

“)  Transverse  section  of  enamel,  the  axial  portion  of  the  prisms  having 
been  removed  by  dilute  hydrochloric  acid. 


THE  DENTAL  TISSUES. 


67 


a  central  narrow  canal  has  sometimes  been  observed  in  the 
interior  of  an  enamel  fibre. 


Fig.  23  d). 


In  fractured  enamel,  the  line  of  fracture  is  said  to  run 
through  the  centre  of  the  fibres,  and  not,  as  might  have 
been  expected,  through  their  interspaces ;  but  this  I  have 
not  verified. 

(i)  Cavities  in  human  enamel,  which  communicate  with  the  dentinal 
tubes. 


Z8 


A  MANUAL  OF  DENTAL  ANATOMY. 


There  is  also  an  appearance  of  striation  upon  a  far  larger 
scale,  consisting  of  brownish  lines,  which  are  never,  or  very 
rarely,  quite  parallel  with  the  outer  surface  of  the  enamel, 
but  which  nevertheless  preserve  some  sort  of  parallelism 
with  it  and  the  surface  of  the  dentine.  These  are  known 
as  the  “  brown  striae  of  Retzius,”  and,  as  they  coincide  with 
what  was  at  one  time  the  outer  surface  of  the  enamel  cusp, 
are  in  some  sense  marks  of  its  stratification  in  its  original 
deposition. 

Pigment  is  seen  in  the  enamel  of  many  rodents  ;  it  is  in 
the  outer  layers  of  the  enamel,  but  has  no  sharply  defined 
boundary,  hiding  away  gradually  into  the  colourless  tissue 
lying  within  it.  Some  authors  have  supposed  that  the  pig¬ 
ment  lay  in  a  thin  coating  of  cementum,  or  in  a  very  dis¬ 
tinct  layer  of  enamel,  but  as  has  just  been  stated,  such  is 
not  the  case. 

Cavities  of  irregular  form  sometimes  exist  in  the  enamel 
near  to  the  surface  of  the  dentine,  and  when  such  spaces 
exist  the  dentinal  tubes  sometimes  communicate  with  them, 
but  these  are  perhaps  to  be  regarded  as  pathological  ; 
Bodecker  regards  them  as  filled  up  by  protoplasm.  Irregular 
fissures  and  cavities  also  occur  upon  the  outer  surface  of  the 
enamel,  which  also  have  no  special  significance  save  as  pre¬ 
disposing  causes  of  dental  caries. 

In  man,  however,  dentinal  tubes  may  occasionally  be  seen 
to  enter  the  enamel,  passing  across  the  boundary  between 
the  two  tissues,  and  pursuing  their  course  without  being  lost 
in  irregular  cavities,  though  this  appearance  is  seldom  to  be 
found.  As  was  pointed  out  by  my  father,  the  passage  of  the 
dentinal  tubes  into  and  through  a  great  part  of  the  thickness 
of  the  enamel  takes  place  in  marsupials  with  such  constancy 
as  to  be  almost  a  class  characteristic. 

The  only  exception  to  the  rule  amongst  recent  marsupials 
occurs  in  the  wombat,  in  which  no  dentinal  tubes  enter  the 
enamel  ;  those  extinct  marsupials  which  have  been  examined 


7 IIE  DENTAL  TISSUES. 


59 


Fig.  24  (1). 


(')  Enamel  and  dentine  of  a  Kangaroo  {Macropus  major). 

The  dentinal  tubes  in  the  dentine  (A)  are  furnished  with  numerous 
short  branches  at  the  line  of  juncture  with  the  enamel ;  they  are  dilated, 
and  a  little  bent  out  of  their  course,  while  beyond  the  dilatation  they  pass 
on  through  about  two-thirds  of  the  thickness  of  the  enamel  in  a  straight 
cjurse  and  without  branches.  Only  a  part  of  the  whole  thickness  of  the 
enamel  is  shown  in  the  figure. 


60 


A  MANUAL  OF  DENTAL  ANATOMY. 


present,  as  might  have  been  expected,  a  structure  in  this 
respect  similar  to  that  of  their  nearest  allies  amongst  the 
recent  genera. 

The  enamel  of  the  wombat  is  peculiar  also  in  another 
respect,  being  covered  by  a  strong  and  remarkably  uniform 
layer  of  cementum. 

The  penetration  of  the  enamel  by  dentinal  tubes  is  not, 
however,  a  peculiarity  quite  confined  to  the  marsupials,  for 
it  is  to  be  found  in  some  rodents  (e.g.  the  jerboa),  and  in 
some  insectivora  ( e.g .,  the  Sorickbe). 

Waldeyer  and  Hertz  doubt  the  passage  of  the  tubes  of  the 
dentine  into  the  enamel ;  as  I^olliker  observes,  it  is  difficult 
to  see  how  they  can  doubt  it,  even  after  mere  observation  of 
a  single  specimen  ;  moreover,  it  is  also  capable  of  experi¬ 
mental  demonstration,  for  if  an  acid  capable  of  removing  the 
enamel  be  applied  to  one  of  these  sections  of  marsupial  teeth 
so  as  to  dissolve  away  the  enamel,  the  freed  tubes  are  left 
hanging  out  from  the  edge  of  the  dentine,  thus  putting  the 
matter  beyond  all  possibility  of  doubt.  The  enamel  is  also 
penetrated  by  dentinal  tubes  in  some  deep  sea  fishes. 

The  most  marked  variation  in  the  structure  of  enamel, 
which  is  on  the  whole  a  tissue  differing  but  little  in  various 
animals,  is  met  with  in  the  class  of  fish. 

In  the  Sargus,  or  sheep’s-head  fish,  for  example,  the  enamel 
is  penetrated  by  a  system  of  tubes  which  are  not  continued 
out  of  or  derived  from  the  dentine,  but  belong  to  the  enamel 
itself. 

The  tubes,  as  seen  in  the  figure,  run  at  right  angles  to 
the  external  surface  of  the  enamel,  proceed  inwards  without 
branch  or  bend  for  some  little  distance,  and  then,  at  about 
the  same  point,  bend  abruptly  at  an  angle,  and  give  off 
numerous  branches.  The  meshwork  produced  by  the  cross¬ 
ing  of  the  tubes  at  all  sorts  of  angles  in  the  inner  part  of 
the  enamel  is  so  complicated  as  to  render  it  impracticable 
to  reproduce  it  in  a  drawing.  That  portion  of  enamel  next 


THE  DENTAL  TISSUES. 


61 


to  the  dentine  is  without  canals.  Yon  Boas  (Zeits.  f.  wissen. 
Zoolog.,  Bd.  xxxii.),  describing  the  similarly  constructed 
enamel  of  scaroid  fishes,  says  that  I  was  in  error  in  sup¬ 
posing  that  the  canals  open  upon  the  outer  surface  of  the 
enamel.  But  I  do  not  understand  his  reasons  for  dissenting 


Fig.  25  (*). 


from  my  opinion,  which  re-examination  of  many  specimens 
has  tended  to  confirm.  I  have  not  been  able  to  satisfy 

c / 

myself  whether  the  tubes  occupy  the  interspaces  of  the 
enamel  prisms,  or  their  axes. 

It  would  appear  also  . as  if  these  tubes  were  empty  during 
life,  as  in  sections  they  appear  to  be  more  or  less  blocked  up 
with  dirt.  The  existence  of  the  prisms  at  all  is  not  certain, 
and  this  led  Kolliker  to  say  that  true  enamel  does  not 
appear  to  exist  in  fishes  (Mik.  Anat.  p.  114) ;  the  enamel  of 
fish  is,  however,  developed  from  an  enamel  organ  homologous 
with,  and  exactly  like,  that  of  amphibia  and  reptiles,  so 
that  these  anomalous  tissues  must  be  regarded  as  being  un¬ 
questionably  enamel. 

(l)  Enamel  and  dentine  of  the  Sheep’s-head  fish  ( Sccrgus  ovis). 

The  enamel  is  penetrated  by  a  system  of  channels  which  enter  from  its 
free  exposed  surface,  pass  in  for  a  certain  distance  in  straight  lines,  and 
then  abruptly  bending  at  an  angle  cross  one  another,  and  produce  a  com¬ 
plicated  pattern  in  the  inner  third  of  the  enamel. 


62 


A  MANUAL  OF  DENTAL  ANATOMY. 


DENTINE. 

The  dentine  makes  up  the  greater  part  of  every  tooth 
which  thus,  even  after  the  removal  of  the  other  tissues, 
would  preserve  somewhat  its  characteristic  form.  Several 
varieties  of  dentine  exist  in  which  those  peculiarities  of 
structure  which  differentiate  it  from  bone  are  less  marked, 
so  that  a  point  is  sometimes  reached  at  which  it  is  hard  to 
say  whether  a  particular  structure  should  more  rightly  be 
regarded  as  dentine,  or  as  bone.  It  will  be  most  convenient 
to  commence  with  thq  description  of  that  variety  of  dentine 
which  differs  most  markedly  from  bone  ;  in  other  words, 
which  has  the  most  typical  “  dentinal  ”  structure  ;  and  for 
that  purpose  the  tissue  met  with  in  the  teeth  of  man  and 
the  majority  of  mammalia,  (though  it  is  by  no  means  con¬ 
fined  to  that  class,)  and  known  under  the  name  “  hard  ”  or 
“  un vascular  ”  dentine,  may  be  selected. 

Dentine  is  a  hard,  highly  elastic  substance,  in  colour 
white  with  a  slight  tinge  of  yellow,  and  to  some  extent 
translucent,  its  transparency  being  often  made  more  striking 
by  contrast  with  the  opacity  which  marks  the  first  advent  of 
dental  caries.  When  broken  a  silky  lustre  is  seen  upon  the 
fractured  surfaces,  which  being  in  the  main  due  to  the 
presence  of  air  in  its  tubes,  is  more  apparent  in  dry  than  in 
fresh  dentine  ;  its  fracture  is  sometimes  described  as  finely 
fibrous. 

The  mass  of  the  dentine  consists  of  an  organic  matrix 
richly  impregnated  with  calcareous  salts  ;  this  matrix  is 
everywhere  permeated  by  parallel  tubes,  which  run,  with 
some  deviations,  in  a  direction  at  right  angles  to  the  surface 
of  the  tooth. 

The  Matrix. — The  exact  chemical  composition  of  the 
matrix  is  not  known  :  in  man  the  proportion  borne  by  the 
organic  to  the  inorganic  constituents  varies  in  different 
individuals,  and  very  probably  in  the  same  individual  at 


TIIE  DENTAL  TISSUES. 


63 


different  ages,  so  that  analyses  can  only  give  approximate 
results.  In  a  fresh  human  tooth  62  per  cent,  of  its  weight 
was  found  to  be  inorganic  salts,  the  tooth  cartilage  being  28 
per  cent.,  leaving  a  residue  of  10  per  cent,  of  water. 

Von  Bibra  gives  the  following  analysis  of  perfectly  dried 
dentine  : — 


Organic  matter  (tooth  cartilage) 
Fat 

Calcium  phosphate,  and  fluoride 
Calcium  carbonate 
Magnesium  phosphate 
Other  salts  .... 

Yon  Bibra  gives  another  analysis  : — 

Cartilage  ..... 
Fat  ..... 
Salts  .  .  . 

Magnesium  phosphate  . 

Calcium  phosphate,  and  fluoride 
Calcium  carbonate  . 

And  Berzelius  gives 

Gelatine  and  water  . 

Sodium  salts  .  .  % 

Magnesium  phosphate 
Calcium  phosphate 
Calcium  fluoride 
Calcium  carbonate 


27-61 

0-40 

66-72 

3-36 

1-18 

0-83 


20-42 

•58 

1-00 

2-49 

67-54 

7*97 


28-00 

1*50 

1-00 

62-00 

2-00 

5-50 


The  dentine  of  many  mammals  is  very  much  more  rich 
in  magnesium  phosphate  than  human  dentine  is ;  even 
the  latter,  it  would  seem,  from  the  discrepancies  existing 
between  the  various  analyses,  is  variable  in  composition, 
but,  on  the  whole,  it  may  be  said  that,  amongst  inorganic 


Da.  a.  WALTEfc 


<54 


A  MANUAL  OF  DENTAL  ANATOMY. 


constituents  of  dentine,  calcium  phosphate  largely  prepon¬ 
derates  ;  from  3|  to  8  per  cent,  consists  of  calcium  carbo¬ 
nate  ;  a  much  smaller  proportion  consists  of  magnesium 
phosphate,  while  calcium  fluoride  exists  in  traces  only. 

The  organic  basis  of  the  matrix  is  closely  related  to  that 
of  bone,  with  which  however  it  is  not  identical ;  it  is  of 
firmer  consistence,  and  does  not  really  yield  gelatine  on 
boiling,  but,  according  to  Kolliker  (who  quotes  Hoppe),  the 
dentine  of  the  pig  yields  a  substance  resembling  glutin, 
the  dentinal  globules  remaining  undissolved.  The  animal 
basis  of  the  dentine  is  called.  “  dentine  cartilage,”  and  is 
readily  obtainable  by  submitting  a  tooth  for  several  days  to 
the  action  of  diluted  acids.  The  form  and  most  of  the 
structural  characteristics  of  a  tooth  so  treated  are  main¬ 
tained,  the  dental  cartilage  forming  a  tough,  flexible,  and 
elastic  semi-transparent  mass. 

In  the  matrix  of  a  perfect  tooth  no  trace  of  cellular 
structure  can  be  detected ;  it  is  uniform  and  perfectly 
transparent. 

The  Dentinal  Tubes. — As  has  been  already  mentioned, 
the  matrix  is  everywhere  permeated  by  tubes,  the  precise 
direction  of  which  varies  in  different  parts  of  the  tooth, 
so  that  the  following  description  of  their  course  must  be 
taken  as  merely  in  a  general  way  descriptive,  and  not  as 
of  universal  or  precise  application.  Each  tube  starts  by  an 
open  circular  mouth  upon  the  surface  of  the  pulp  cavity ; 
thence  it  runs  outwards,  in  a  direction  generally  per¬ 
pendicular  to  the  surface,  towards  the  periphery  of  the 
dentine,  which,  however,  it  does  not  reach,  as  it  becomes 
smaller,  and  breaks  up  into  branches  at  a  little  distance 
beneath  the  surface  of  the  dentine. 

Near  to  the  pulp  they  are  so  closely  packed  that  there  is 
little  room  between  them  for  the  matrix,  while  near  to  the 
outside  of  the  tooth  they  are  more  widely  separated  :  their 
diameter  is  also  greater  near  to  the  pulp  cavity. 


THE  DENTAL  TISSUES. 


65 


The  dentinal  tubes  do  not  pursue  a  perfectly  straight 
course,  but  describe  curves  both  on  a  larger  and  a  smaller 
scale.  The  longer  curves  are  less  abrupt  than  the  others, 
and  are  termed  the  “  primary  curvatures ;  ”  they  are  often 
compared  to  the  letter  /,  to  which  they  bear  a  certain 
amount  of  resemblance ;  the  primary  curves  are  more 
pronounced  in  the  crown  than  in  the  root. 


Fig.  26  ('). 


The  secondary  curvatures  are  very  much  more  numerous 
and  are  smaller  ;  the  actual  course  of  the  dentinal  tube  is, 
in  many  places  at  all  events,  an  elongated  spiral,  as  may 
be  very  well  seen  in  thick  sections  transverse  to  the  tubes  ; 
by  alterations  in  the  focus  of  the  microscope  the  appearance 
of  the  tube  making  a  spiral  turn  is  made  very  striking. 
The  effect  of  an  elongated  spiral  viewed  on  its  side  will  of 
course  be  only  slight  undulations,  such  as  are  the  secondary 
curvatures  of  the  tubes.  The  spiral  course  of  the  dentinal 
tubes  is  most  strongly  marked  in  the  roots  of  teeth. 

(*)  Dentine  and  c^mentum  of  a  Narwal,  showing  contour  lines  due  to 
rows  of  interglobular  spaces. 


F 


66 


A  MANUAL  OF  DENTAL  ANATOMY. 


When  a  transverse  section  of  dentine  is  viewed,  bands  or 
rings,  concentric  with  the  pnlp  cavity,  are  seen,  and  the  same 
bands  may  be  seen  in  longitudinal  section.  Such  a  striated 
or  laminated  appearance  in  the  dentine  may  be  due  to  two 
causes ;  and  some  little  confusion  has  arisen  in  the  nomen¬ 
clature,  owing  to  its  double  origin  not  having  always  been 
kept  in  view.  Such  strim  may  be  due  to  the  presence  of 
rows  of  interglobular  spaces,  or  to  the  coincidence  of  the 
primary  curvatures  of  neighbouring  dentinal  tubes  :  that 
is  to  say,  each  tube  bends  at  the  same  distance  from  the 
surface,  and  the  bend  makes  a  difference  in  the  optical  pro¬ 
perties  of  the  dentine  at  that  point. 

Schreger  described  these  latter :  the  lines  of  Sclireger, 
therefore,  are  markings,  ranged  parallel  with  the  exterior  of 
the  dentine,  which  are  due  to  the  curvatures  of  the  dentinal 
tubes. 

The  “  contour  lines  ”  of  Owen,  even  in  his  own  works, 
include  markings  of  both  classes  :  i.  e.,  those  due  to  the 
curvature  of  the  dentinal  tubes,  and  those  due  to  lamina)  of 
interglobular  spaces,  such  as  are  met  with  in  the  teeth  of 
Cetacea.  Retzius  had  seen  and  described  contour  markings 
due  to  interglobular  spaces,  though  his  name  is  not  usually 
associated  with  them,  the  “  brown  striae  of  Retzius  ’’  being 
markings  in  the  enamel. 

The  tubes  as  they  pass  outwards  often  divide  into  two 
equally  large  branches ;  they  also  give  off  fine  branches, 
which  anastomose  with  those  of  neighbouring  tubes.  In  the 
crown  of  a  human  tooth  these  fine  branches  are  compara¬ 
tively  few,  until  the  tube  has  reached  nearly  to  the  enamel, 
but. in  the  root  they  are  so  numerous  as  to  afford  a  ready 
means  of  distinguishing  whence  the  section  has  been  taken. 
The  small  branches  above  alluded  to  are  given  off  at  right 
angles  to  the  course  of  the  main  tube,  which,  however,  itself 
frequently  divides  and  subdivides,  its  divisions  pursuing  a 
nearly  parallel  course. 


THE  DENTAL  TISSUES. 


67 


The  tubes  are  subject  to  slight  varicosities,  and  their 
course  is  sometimes  apparently  interrupted  by  a  small  inter- 
globular  space,  as  is  to  be  seen  in  an  extreme  degree  in  the 
dentine  of  Cetacea. 

Owing  to  their  breaking  up  into  minute  branches,  some 
of  the  tubes  become  lost  as  they  approach  the  surface  of  the 
dentine,  and  apparently  end  in  fine  pointed  extremities. 

Some  terminate  by  anastomosing  with  terminal  branches 
of  others,  forming  loops  near  to  the  surface  of  the  dentine  ; 
others  terminate  far  beneath  the  surface  in  a  similar  way. 


Fig.  27  ( 1 ). 


Some  tubes  pass  into  the  small  interglobular  spaces 
which  constitute  the  “granular  layer”  described  by  my 
father,  vrhile  others  again  pass  out  altogether  beyond  the 
boundary  of  the  dentine  and  anastomose  with  the  canaliculi 
of  the  lacume  in  the  cementum. 

The  enamel  also  may  be  penetrated  by  the  dentinal 
tubes,  though  this  when  occurring  in  the  human  subject 
must  be  regarded  as  exceptional  and  almost  pathological 
in  its  nature  (see  Fig.  23).  As  has,  however,  been  men¬ 
tioned  in  speaking  of  the  enamel,  in  most  of  the  Marsupials 
and  in  certain  other  animals  it  is  a  perfectly  normal  and 
indeed  characteristic  occurrence,  difficult  though  it  be  to 
see  howr  such  a  relation  of  parts  is  brought  about  in  the 
course  of  development  of  the  two  tissues. 

(')  Termination  of  a  dentinal  tube  in  the  midst  of  the  dentine — human. 


68 


A  MANUAL  OF  DENTAL  ANATOMY. 


Bentinal  Sheaths. — If  dentine  be  exposed  to  the  action 
of  strong  acid  for  some  days,  a  sort  of  fibrous  felt,  or  if  the 
action  of  the  acid  has  gone  further,  a  transparent  slime  alone 
remains.  Examined  with  the  microscope  this  proves  to  be  a 
collection  of  tubes  ;  it  is,  in  fact,  made  up  of  the  immediate 
walls  of  the  dentinal  tubes,  the  intervening  matrix  having 
been  wholly  destroyed. 

Two  facts  are  thus  demonstrated  :  the  one  that  the  tubes 
have  definite  walls,  and  are  not  simple  channels  in  the 
matrix ;  the  other,  that  these  walls  are  composed  of  some¬ 
thing  singularly  indestructible.  Indeed,  the  walls  of  the 
dentinal  tubes  are  so  indestructible  that  they  may  be 
demonstrated  in  fossil  teeth,  in  teeth  boiled  in  caustic 
alkalis,  or  in  teeth  which  have  been  allowed  to  putrefy. 

Although  Kolliker  was,  I  believe,  the  first  to  describe  and 
figure  these  isolated  tubes,  they  are  generally  known  as  the 
“  dentinal  sheaths  of  Neumann,”  the  latter  writer  having 
more  fully  investigated  and  described  them.  The  precise 
chemical  nature  of  these  sheaths  will  be  more  conveniently 
considered  under  the  head  of  calcification  :  similarly  inde¬ 
structible  tissues  are,  however,  to  be  met  with  surrounding 
the  Haversian  canals  and  the  lacunae  of  bone.  It  is  the 
opinion  of  Neumann,  as  it  was  also  of  Henle,  that  the 
dentinal  sheaths  are  calcified  ;  but  the  proof  of  this  is 
very  difficult,  as  they  cannot  be  demonstrated,  or  I  should 
rather  say,  isolated,  to  any  extent  in  dentine,  unless  it  has 
been  decalcified.  Their  existence  as  distinct  from  the  fibrils 
has  been  recently  denied  by  Magitot  and  by  Dr.  Sudduth. 

Transverse  sections  of  dentine  present  fallacious  appear¬ 
ances,  owing  to  the  thickness  of  the  section  giving  to  the 
tube  a  double  contour  which  may  be  easily  mistaken  for  a 
special  wall.  Immediately  round  the  opening  of  the  canal, 
or  “lumen,”  as  it  is  called,  there  is  however  generally  a  thin 
yellowish  border,  which  may  perhaps  be  the  sheath  of  Neu¬ 
mann.  Tn  the  earlier  stages  of  caries,  before  the  dentine  is 


THE  DENTAL  TISSUES. 


69 


much  softened,  the  walls  of  the  canals  become  strikingly  appa¬ 
rent.  But  it  must  be  remembered  that  the  dentinal  sheaths 
can  only  be  demonstrated  by  processes  which  amount  to  a 
partial  destruction  of  the  dentine,  and  they  are  therefore  in 
some  degree  at  all  events  artificial,  and  it  may  be  that  they 
have  no  real  existence  until  they  are  brought  into  existence 
by  the  action  of  these  agents.  In  that  case  all  that  we  are 


Fig.  28  (')• 


entitled  to  say,  is,  that  the  immediate  surroundings  of  the 
soft  fibril  differ  somewhat  in  chemical  constitution  from  the 
parts  of  the  matrix  which  are  more  remote,  and  so  that 
under  the  action  of  destructive  agents  the  matrix  may  be 
split  up  into  the  sheathing  layers  round  the  fibrils  and  the 
more  soluble  residuum  of  the  matrix. 

Dentine  would  thus  be  considered  as  a  tissue  made  up  of 
a  calcified  matrix,  analogous  to  that  of  bone,  permeated  by 
the  soft  fibril  just  as  bone  is  permeated  by  canaliculi  with 
soft  contents,  but  having  this  peculiarity,  that  the  latest 
formed  portions  of  matrix,  namely,  those  immediately  em¬ 
bracing  the  fibrils,  differed  sufficiently  from  the  bulk  of 
the  matrix  in  chemical  constitution  to  enable  them  to  be 
isolated  as  sheathing  tubes. 

The  canals  which  everywhere  permeate  the  dentine  are 
not  empty,  a  fact  which  might  be  inferred  from  the  differ¬ 
ence  in  translucency  and  general  aspect  of  dry  and  fresh 

x)  Transverse  section  of  dentine.  The  appearance  of  a  double  contour 
is  so  much  exaggerated  as  to  make  the  figure  diagrammatic. 


70 


A  MANUAL  OF  DENTAL  ANATOMY. 


dentine,  whether  seen  in  mass  or  in  thin  section  ;  neither 
are  they,  as  was  at  one  time  supposed,  tenanted  merely  by 
fluid. 

Bentinal  Fibrils. — Each  canal  is  occupied  by  a  soft 
fibril,  which  is  continuous  with  a  cell  upon  the  surface  of 
the  pulp ;  the  existence  of  these  soft  fibrils  was  first  demon¬ 
strated  by  my  father,  who  thus,  to  use  the  words  of 


Fig.  29  (b. 


Waldeyer,  “  opened  the  way  to  a  correct  interpretation  of 
the  nature  of  the  dentine.” 

Henle,  in  his  “  Allgemeine  Anatomie,”  (1841),  a  transla¬ 
tion  of  a  portion  of  which  is  to  be  found  in  the  “  Archives 
of  Dentistry,”  (1865),  figured  and  described  projections  from 
the  edges  of  fragments  of  dentine  in  continuity  with  the 
dentinal  tubes.  These  he  distinctly  describes  as  calcified  and 
rigid ,  adding  that  by  the  use  of  acids  they  may  be  made 
flexible ;  he  speaks  of  the  tube  as  empty,  save  when  blocked 
by  granular  calcareous  matter,  and  alludes  to  fluids  entering 
it  by  capillarity ;  and  lastly,  he  says  nothing  whatever  of 
the  connections  of  the  pulp  with  the  tubes. 

Muller,  (as  translated  in  Nasmyth  on  the  “  Structure  of 
the  Teeth,”  1839),  says,  “  in  breaking  fine  sections  of  the 
teeth  perpendicularly  to  the  fibres,  he  has  frequently  seen  the 

P)  A  fragment  of  dentine  (a),  through  which  run  the  softer  fibrils  (c), 
which  are  seen  to  be  continuous  with  the  odontoblast  cells  ( b ).  (After 
Dr.  Lionel  Beale.) 


THE  DENTAL  TISSUES. 


71 


latter  projecting  a  little  at  the  fractured  edge.  In  such 
cases  they  are  quite  straight  and  not  curved,  and  seem 
to  be  not  at  all  flexible.  Hence  it  follows  that  the  tubes 
have  an  organised  basis,  a  membrane,  and  that  this  is  stiff 
and  brittle,  and  probably  saturated  with  calcareous  salts, 
but  weak  and  soft  in  a  decalcified  tooth.” 

The  whole  importance  of  my  father’s  discovery  lay  in  the 
fact  that  dentine  is  permeated  by  soft,  uncalcified  structures  ; 
and  what  is  yet  more  significant,  that  these  soft  fibrils,  per¬ 
meating  the  hard  dentine,  proceed  from  the  pulp.  In  no 
sense,  therefore,  did  Henle  anticipate  this  discovery. 

In  1854  Lent  figured  processes  from  the  dentinal  cells 
(odontoblasts)  which  he  rightly  conceived  to  be  concerned 
in  the  formation  of  dentine  ;  but  in  the  earlier  editions  of 
the  “Histology”  of  his  friend  and  teacher,  Prof.  Kolliker, 
although  Lent’s  discoveries  are  described  and  adopted  with¬ 
out  reservation,  no  mention  of  the  real  structure  of  dentine 
occurs.  But  in  the  last  edition,  Prof.  Kolliker  says — “  after 
Tomes  had  described  a  soft  fibre  in  each  tube,  I  fell  into  the 
mistake  of  supposing  that  these  fibres  and  the  tubes  were 
one  and  the  same.” 

The  circumstances  under  which  the  dentinal  fibrils  can 
or  cannot  be  discovered  are  as  follows,  and  may  be  taken  as 
indications  of  a  distinction  between  the  dentinal  fibrils  and 
the  dentinal  sheaths. 

If  a  tooth  section  be  submitted  to  the  action  of  a  ‘caustic 
alkali  and  boiled  in  it,  or  be  allowed  to  completely  putrefy, 
so  that  the  soft  parts  are  entirely  destroyed,  the  dentinal 
sheaths  can  still  be  demonstrated,  but  the  fibres  can  in  no 
way  be  brought  into  view  (Kolliker).  The  dentinal  sheaths 
may  be  demonstrated  also  in  fossil  teeth,  as  has  been  shown 
by  Hoppe  (Wurzburg  Nat.  Zeitschrift,  Bd.  VI.  p.  xi.)  and 
others. 

In  fresh  dentine  every  formative  cell  sends  a  process  into 
the  dentinal  tubes  (Tomes,  Kolliker,  Lent,  Waldeyer,  Neu- 


72 


A  MANUAL  OF  DENTAL  ANATOMY . 


mann),  and  it  has  been  found  possible  to  demonstrate  both 
the  sheaths  and  the  fibres  in  the  same  sections  (Neumann, 
Boll). 

In  transverse  and  even  in  longitudinal  sections  of  decalci¬ 
fied  dentine  the  fibrils  may  be  recognised  in  situ  (Kolliker). 

The  contrast  between  the  dentinal  sheaths  and  the  fibrils 
is  this  : — the  sheaths  are  very  indestructible,  and  can  be 
demonstrated  in  teeth  which  have  undergone  all  sorts  of 
change ;  the  soft  fibril  is  no  longer  demonstrable  when  the 
tooth  has  been  placed  in  circumstances  which  would  lead 


Fm.  30  (»). 


to  its  soft  parts  perishing.  In  dentine,  then,  we  have  (i.)  a 
matrix  permeated  by  canals  ;  (ii.)  special  walls  to  these  canals 
or  “  dentinal  sheaths ;  ”  and  (iii.)  soft  fibrils  contained  in 
these  canals,  or  “  dentinal  fibres  ;  ”  and  it  now  remains  to 
consider  these  in  farther  detail. 

In  fortunate  sections  of  small  fragments  of  dentine  taken 
from  the  edges  of  the  pulp  cavity  and  including  the  surface 
of  the  pulp,  the  dentinal  fibrils  may  be  seen  stretching  from 
the  cells  of  the  superficial  layer  of  the  pulp  (odontoblasts) 
into  the  dentinal  tubes,  as  owing  to  these  being  extensile 
they  may  be  stretched  or  drawn  out  from  the  tubes  for  some 
little  distance  without  being  broken  across.  In  the  same 
vTay  they  may  be  seen  stretching  across  like  harp-strings 
between  two  pieces  of  dentine,  w’hen  this  is  torn  by  needles, 

(’)  Section  of  dentine  from  the  edge  of  which  hang  ont  the  dentinal 
sheaths,  and  beyond  these  again  the  fibrils  (after  Boll). 


THE  DENTAL  TISSUES. 


73 


and  they  can  be  thus  shown  in  fresh  fragments  just  as  well 
as  in  those  of  decalcified  dentine.  When  stretched  to  a 
considerable  extent  their  diameter  becomes  diminished  and 
they  finally  break,  a  sort  of  bead  sometimes  appearing  at  the 
broken  end  (Tomes).  This  would  seem  to  indicate  that  the 
substance  of  the  fibril  is  of  colloid  consistency,  and  that  its 
external  portions  are  in  some  degree  firmer  than  its  axial 
portion. 

The  dentinal  fibrils  are  well  seen  in  the  accompanying 
figure,  in  which  some  hong  out  from  the  edge  of  the  dentine. 


Fig.  31  (J)'. 


whilst  others  have  been  pulled  out  from  the  dentine  and  are 
seen  attached  to  the  odontoblast  cells. 

The  dentinal  fibril  is  capable  of  being  stained  with  car¬ 
mine,  though  with  some  difficulty  ;  in  young  dentine  it 
is  more  easily  stained,  especially  near  the  pulp  cavity,  and 
the  accompanying  drawing  is  taken  from  such  a  section  of 
dentine  from  a  half  formed  human  incisor.  The  matrix  is 
slightly  stained  with  the  carmine,  indicating  that  it  has  not 

0)  Surface  of  the  pulp,  with  the  odontoblast  layer  in  situ.  The  dentine 
fibrils  pulled  out  of  the  dentinal  tube  hang  like  a  fringe  from  the  odonto¬ 
blast  layfer  :  dentine  fibrils  are  also  seen  hanging  out  from  the  edge  of  the 
dentine,  to  which,  to  the  right  of  the  figure,  a  few  odontoblasts  remain 
attached. 


74 


A  MANUAL  OF  DENTAL  ANATOMY. 


yet  become  fully  impregnated  with  salts,  and  in  the  centres 
of  the  clear  areas  dark  spots  deeply  stained  with  carmine 
are  to  be  seen,  the  latter  being  transverse  sections  of  the 
dentinal  fibrils  in  situ.  I  have  observed  precisely  similar 
appearances  in  the  thin  young  dentine  of  calves’  and  pigs’ 
teeth  ;  Kolliker  also  mentions  that  the  dentinal  fibril  may 
be  recognised  in  situ  in  transverse  sections  of  fresh  dentine. 

Bodecker  finds  that  the  dentinal  fibrils  stain  darkly  with 
chloride  of  gold ;  when  viewed  in  transverse  sections  under 


Fig.  32  [}). 


a  magnifying  power  of  2,000  diameters  they  do  not  appear 
round  but  somewhat  angular,  and  give  off  tiny  lateral 
offshoots  which  seem  to  penetrate  the  dentine.  In  the 
matrix  itself  there  is  an  appearance  of  a  faint  network  when 
it  has  been  stained  with  gold,  and  from  this  Bodecker  infers 
that  the  dentine  is  penetrated  everywhere  by  a  network 
of  living  plasm,  derived  from,  though  far  finer  than,  the 
dentinal  fibrils. 

Probably  the  angularity  of  the  fibril,  which,  as  figured  by 
him,  is  much  smaller  than  the  canal,  is  due  to  its  having 
shrunk  under  the  action  of  chromic  acid  or  some  such 
reagent. 

According  to  Neumann,  in  old  age  the  fibrils  atrophy  or 
become  calcified ;  some  observers  have  failed  to  detect  them 

(l)  Transverse  section  of  dentine  ;  in  four  of  the  dentinal  tubes,  the 
dentinal  fibrils  deejjly  stained  with  carmine,  in  the  preparation  from  which 
this  figure  was  drawn,  are  seen.  The  fibrils  are  somewhat  shrunken, 
owing  to  the  action  of  the  glycerine  in  which  the  section  is  mounted. 


THE  DENTAL  TISSUES. 


75 


near  to  the  periphery  of  the  dentine,  far  away  from  the  pulp 
cavity.  But  here  they  would  naturally  be  more  minute, 
and  it  is  more  probable  that  the  manipulations  had  failed 
to  demonstrate  them  than  that  they  were  absent ;  for 
Bodecker  has  traced  them  to  the  very  outside  of  the 
dentine. 

Dr.  Beale  has  seen  prolongations  of  the  nucleus  of  the  cell 
towards  the  base  of  the  fibril,  though  in  the  example  which 
he  figures  it  does  not  enter  it. 

Dentinal  fibrils  have  been  demonstrated  in  the  Beptilia 
and  Amphibia  by  Santi  Sirena  and  myself ;  and  by  myself 
in  the  few  fish  that  I  have  examined  with  that  purpose. 

Of  their  real  nature  some  doubts  are  entertained  :  they 
are  certainly  processes  of  the  cells  of  the  pulp,  and  their  sub¬ 
stance  seems  identical  with  that  of  the  protoplasm  of  the 
cell.  Nerves,  in  the  ordinary  sense  of  the  word,  they  are 
not,  and  have  never  been  supposed  to  be  ;  but  there  are 
many  examples  of  cellular  structures  which  are  connected 
with  the  termination  of  sensory  nerve  fibres,  such  as  the 
goblet  cells  in  the  olfactory  membrane  of  the  frog,  and  it  is 
quite  possible  that  the  odontoblast  cells  may  stand  in  some 
such  relations  to  the  nerves  of  the  pulp,  the  terminations  of 
wdiich  have  never  been  satisfactorily  traced. 

Mr.  Coleman  once  suggested  that  it  was  possible  that 
the  odontoblasts  might  have  some  tactile  function,  and  Mr. 
Hopewell  Smith  (“Dental  Becord,”  Aug.,  1889,)  points  out 
their  resemblance  to  multipolar  ganglion  cells  of  the  spinal 
cord.  According  to  Magitot  the  nerves  of  the  pulp  become 
continuous  with  a  layer  of  reticulate  cells  which  lie  beneath 
the  odontoblasts  ;  and  these  freely  communicate  with  the 
processes  of  the  odontoblasts,  so  that  there  is  a  very  direct 
chain  of  communication  between  the  dentinal  fibril  and  the 
nerves  of  the  pulp.  M.  Magitot  speaks  very  positively  as 
to  the  accuracy  of  his  views,  wrhich  as  yet,  however,  have 
not  been  confirmed  by  other  investigators. 


7,6 


A  MANUAL  OF  DENTAL  ANATOMY 


Yet  another  view  of  the  nature  of  the  dentinal  fibril  is 
advocated  by  Klein  (“Atlas  of  Histology,”  p.  183),  who 
holds  that  the  odontoblasts  are  concerned  only  in  the 
formation  of  the  dentine  matrix,  and  that  the  dentinal 
fibrils  are  long  processes  of  the  deeper  cells,  in  the  above 


Fig.  33  l1). 


figure,  which  run  up  between  the  odontoblasts  and  enter 
the  dental  canals. 

In  a  recent  paper  (Comptes  Rendus,  1880,)  Magitot  also 
impugns  the  accuracy  of  the  views  ordinarily  accepted  as  to 
the  structure  of  dentine,  denying  the  existence  of  any 
special  walls  to  the  tubes,  and  further  arguing  that  it  is 
undesirable  to  think  or  speak  of  the  channels  in  dried  dentine 
as  tubes  at  all.  For,  he  argues,  they  are  not  tubes  in  the 
fresh  state,  seeing  that  the  fibrils  are  adherent  to  the 
matrix  and  form  a  part  of  it,  and  that  they  were  originally 
precisely  the  same  tissue.  He  would  prefer  to  speak  of 

(x)  After  Magitot.  a.  Dentinal  fibrils.  b.  Amorphous  matrix, 
e.  Odontoblasts,  d.  Nuclei  of  odontoblasts,  e.  Stellate  cells,  f.  Nerve 
extremities  which  are  continuous  with  the  branched  cells. 


THE  DENTAL  TISSUES. 


77 


dentine  as  being  a  fibrillar  tissue  included  in  a  hard  and 
homogeneous  matrix. 

These  views,  however,  do  not  differ  substantially  from 
those  in  the  text,  save  that  M.  Magitot  does  not  recognise 
the  existence  of  that  transitional  tissue  which  others  believe 
to  be  there,  and  call  the  sheaths  of  Neumann. 

No  true  nerve  fibril  has  ever  been  seen  to  enter  the  den¬ 
tine  ;  nothing  but  the  dentinal  fibril  has  ever  been  proved 
to  pass  from  the  pulp  into  the  hard  substance  of  the 
tooth  ;  nevertheless,  the  observation  of  Boll  is  very  sug¬ 
gestive.  He  found  that  by  treating  a  perfectly  fresh  pulp 
with  |  per  cent,  solution  of  chronic  acid  an  immense 
number  of  fine  fibres  could  be  demonstrated,  a  great  many 
of  which  projected  from  above  the  surface,  as  though  they 
had  been  pulled  out  of  the  dentinal  tubes ;  but  although 
they  pass  up  from  a  plexus  of  dark-bordered  nerve  fibres 
beneath  the  membrana  eboris  between  the  cells  of  that 
layer,  their  passage  into  the  dentine  remains  a  mere  matter 
of  inference. 

Boll’s  observations  likewise  are  awaiting  confirmation  or 
disproof,  and  so  far  stand  alone. 

Be  that  as  it  may,  there  can  be  no  question  that  the 
sensitiveness  of  the  dentine  is  due  to  the  presence  of  soft 
organized  tissue  in  the  tubes,  and  is  not  a  mere  transmission 
of  vibrations  to  the  pulp  through  a  fluid  or  other  inert 
conductor.  The  peripheral  sensitiveness  of  a  tooth  can  be 
allayed  by  local  applications  which  it  would  be  absurd  to 
suppose  were  themselves  conducted  to  the  pulp  ;  moreover, 
it  is  within  the  experience  of  every  operator  that  after  the 
removal  of  a  very  sensitive  layer  of  caries,  you  often 
come  down  upon  dentine,  which,  though  nearer  to  the 
pulp,  is  fiir  less  sensitive,  a  condition  quite  inexplicable, 
except  upon  the  supposition  of  a  different  local  condition 
of  the  contents  of  the  tubes.  Irritation  applied  to  the 
dentinal  fibrils  may  be  propagated  to  the  pulp,  and  irri 


A  MANUAL  OF  DENTAL  ANATOMY. 


78 


tation  of  the  pulp  set  up  without  any  real  exposure  of  the 
latter. 

With  reference  to  the  probabilities  of  actual  nerve  fibres 
entering  the  dentinal  tubes,  it  must  be  remembered  that,  in 
those  tissues  which  are  naturally  so  thin  as  to  present 
great  facilities  for  examination,  nerves  of  a  degree  of  fine¬ 
ness  unknown  elsewhere  have  been  demonstrated  ;  in  other 
words,  the  easier  the  tissue  is  to  investigate,  the  finer  the 
nerves  which  have  been  seen  in  it,  while  dentine  is  among 


Fig.  34  (*). 


the  most  difficult  substances  conceivable  for  the  demonstra¬ 
tion  of  fine  nerve  fibrils,  if  such  exist  in  it. 

Interglobular  Spaces. — In  the  layer  of  dentine  which 
underlies  the  cement  an  immense  number  of  these  spaces 
exist,  giving  to  the  tissue  as  seen  under  a  low  power  an 
appearance  of  granularity.  On  this  account  my  father  gave 
to  this  the  name  of  the  “granular  layer”  of  dentine;  on 
account  of  the  far  greater  abundance  of  the  spaces  in  that 
situation,  it  is  far  more  marked  beneath  the  cement  than 
beneath  the  enamel,  and  manv  of  the  dentinal  tubes  end  in 
these  spaces. 

Although  the  name  “  interglobular  spaces  ”  is  strictly  ap¬ 
plicable  to  the  structures  constituting  the  granular  layer 
of  dentine,  it  was  not  to  these  that  it  was  first  applied. 
When  a  dried  section  of  dentine  is  examined,  dark  irregular 


(')  Dentinal  tubes  terminating  in  the  spaces  of  the  granular  layer. 


TEE  DENTAL  TISSUES. 


79 


spaces,  clustered  together  and  usually  most  abundant  at  a 
little  distance  below  the  surface,  are  often  to  be  seen,  parti¬ 
cularly  if  the  section  has  been  made  from  a  brownish,  im¬ 
perfectly  developed  tooth. 

These  spaces  have  a  ragged  outline,  furnished  with  short 
pointed  processes,  and  in  favourably-prepared  sections  it 
may  be  seen  that  their  outlines  are  formed  by  portions  of 
the  surfaces  of  closely  opposed  spheres,  and  globular  con¬ 
tours  may  often  be  detected  in  the  solid  dentine  near  to 


Fig.  35  ('*). 


them,  as  is  seen  in  the  accompanying  figure,  taken  from  a 
section  boiled  in  wrax  in  order  to  render  it  very  transparent. 

Although  these  large  spaces  are  very  common,  they  are 
perhaps  not  to  be  regarded  as  perfectly  normal,  but  are 
rather  indications  of  an  arrested  development  at  that  spot. 
The  occurrence  of  globular  forms  during  the  early  stages 
of  calcification,  will  again  be  alluded  to  in  connection  with 
the  development  of  teeth  ;  but  although  the  term  “  inter- 

(*)  Interglobular  spaces  in  dentine. 


80 


A  MANUAL  OF  DENTAL  ANATOMY. 


globular  ”  is  thus  strictly  applicable,  the  use  of  the  'word 
“spaces”  is  not  so  correct.  In  dry  dentine  it  is  true  that 
they  are,  as  Czermak  described  them,  spaces  filled  with  air ; 
but  that  they  are  so  is  only  due  to  the  fact  that  their 
contents  are  soft,  and  shrivel  up  in  drying.  In  the  fresh 
condition  the  interglobular  “  space 77  is  perfectly  full,  its 
contents  often  having  the  structural  arrangement  of  the 
rest  of  the  matrix,  or  else  consisting  of  soft  plasm  ;  in 
the  former  case,  the  dentinal  tubes  pass  across  and  through 


Fig.  36  (1). 


it  without  any  interruption  or  alteration  in  their  course. 
This  fact,  as  well  as  the  soft  nature  of  the  contents  as  com¬ 
pared  with  the  rest  of  the  dentine,  is  well  illustrated  by  a 
section  in  my  possession  which  was  taken  from  a  carious 
tooth,  near  to  the  affected  surface.  In  this  the  fungus, 
(leptothrix  ?),  had  effected  an  entrance  into  some  of  the  tubes 
giving  to  them  a  varicose  beaded  appearance,  and  causing 
their  enlargement.  But  when  it  reached  the  interglobular 
space,  the  less  amount  of  resistance,  or  possibly  the  more 
favourable  pabulum  accessible,  led  to  its  more  rapid  deve¬ 
lopment,  so  that  the  tubes  within  the  confines  of  the  space 
are  many  times  more  enlarged  than  those  outside ;  never¬ 
theless  the  continuity  of  the  tubes  across  the  space  is  well 

(’)  Section  of  carious  dentine,  in  which  some  of  the  tubes  are  headed 
by  the  ingress  of  the  leptothrix,  which  has  developed  with  greater  freedom 
in  one  or  two  of  the  tubes  where  they  cross  the  interglobular  spaces. 


THE  DENTAL  TISSUES. 


81 


demonstrated  by  the  growth  of  leptothrix  having  followed 
them  with  exactitude. 

It  sometimes  happens  that  indications  of  spherical  forms 
and  faintly  discernible  contours  resembling  those  of  the 
interglobular  spaces  may  be  seen  in  dried  sections,  in  which 
no  actual  spaces  occur.  The  appearances  are  perhaps  pro¬ 
duced  by  the  formation  of  an  interglobular  space,  the  con¬ 
tents  of  which  have  subsequently  become  more  or  less 
perfectly  calcified  :  the  term  “  areolar  dentine  ”  sometimes 
applied  to  this  is  falling  into  disuse. 

The  exact  nature  of  the  contents  of  the  interglobular 
spaces  is  not  very  certain  :  they  may,  with  some  difficulty, 
be  tinted  by  carmine,  and  it  is  said  that  they  may,  like 
the  dentinal  sheaths,  be  isolated  by  the  destruction  of  the 
rest  of  the  matrix  in  acids ;  that  this  may  be  done  I  do 
not  doubt,  although  I  have  never  succeeded  in  so  isolating 
them  myself. 

Bodecker  finds  that  there  is  soft  living  plasm  abundantly 
distributed  in  the  smaller  interglobular  spaces  which  con¬ 
stitute  the  granular  layer,  and  that  this  is  in  very  free  com¬ 
munication  with  the  soft  fibrils  in  the  tubes  on  the  one  side, 
and  with  the  soft  contents  of  the  lacunae  and  canaliculi  of 
the  cementum  on  the  other. 

In  the  dentine  so  far  described,  which  is  that  variety  known 
as  hard  or  unvascular  dentine,  some  degree  of  nutrition  is 
perhaps  provided  for  by  the  penetration  of  the  whole  thick¬ 
ness  of  the  tissue  by  protoplasmic  fibres,  the  dentinal  fibrils, 
but  this  nutrition  may  be  effected  in  a  different  way,  and 
there  are  other  varieties  of  dentine  known  in  which  dentinal 
fibrils  have  never  been  shown  to  exist.  For  descriptive 
purposes  I  would  classify  dentines  as 
(i.)  Hard  or  unvascular  dentine. 

(ii.)  Plici-dentine. 

(iii.)  Yaso-dentine. 

(iv.)  Osteo-dentine. 

G 


82  A  MANUAL  OF  DENTAL  ANATOMY. 


Ordinary  hard  dentine  has  been  sufficiently  described ; 
plici-dentine  is  a  variety  of  it  not  very  distinct  in  its  essential 
nature,  though  at  first  sight  widely  dissimilar. 

Plici-dentine. — In  ordinary  dentine  the  dentinal  tubes 
radiate  out  from  a  pulp  and  pulp  chamber  of  simple  form ; 
render  complex  that  form  by  foldings  of  its  walls,  the  den¬ 
tinal  tubes  still  running  off  at  right  angles  to  that  portion 


Fig.  37  (ffi 


of  pulp  to  which  they  immediately  belong,  and  we  have 
a  “  plici-dentine.  ”  It  is  merely  an  ordinary  dentine  with  its 
pulp  folded  up  and  wrinkled  into  a  greater  or  less  degree 
of  complexity. 

In  the  teeth  of  the  Varanus  (monitor  lizard)  the  process  of 
calcification  of  the  pulp  takes  place  in  such  manner  that  in 
the  upper  half  of  the  tooth  a  cap  of  ordinary  unvascular 
dentine,  in  which  the  tubes  radiate  from  a  single  central 

(*)  Section  of  Plici-dentine  with  the  pulp  in  situ  (Lepidosteus). 
o.  Odontoblasts,  p.  Connective  tissue  framework  of  pulp.  d.  Dentine. 


THE  DENTAL  TISSUES. 


83 


pulp  cavity,  is  formed.  But  in  the  lower  part  of  the  tooth 
slight  longitudinal  furrows  appear  on  the  surface,  which,  on 
transverse  section,  are  seen  to  correspond  to  dippings  in  of 
the  dentine  ;  and  the  dentine  is,  as  it  were,  in  folds.  The 
pulp  on  section  might  be  compared  to  a  paddle-wheel,  the 
floats  of  which  correspond  to  the  thin  flat  radiating  pro- 


Fig.  3S  (1). 


cesses  of  pulp ;  but  as  yet  the  central  pulp  chamber  is 
unaltered.  A  little  lower  down,  as  represented  in  the 
accompanying  figure,  there  is  no.  longer  a  central  simple 
pulp  chamber  ;  the  inflections  round  the  periphery  have 
become  relatively  much  deeper,  and  the  centre  of  the  tooth 
is  occupied  by  a  tissue  irregular,  but  not  otherwise  unlike 
the  dentine  of  Myliobates ;  that  is  to  say,  there  are  a 
number  of  columns  of  pulp,  each  of  which  forms  the  axis 
whence  a  system  of  dental  tubes  radiate. 

The  outrunning  plates  of  dental  pulp,  which  on  section 
radiate  out  like  the  spokes  of  a  wheel,  do  not  always  remain 
single ;  they  may  divide  simply  into  two  branches,  as  may 
be  seen  in  the  section  across  the  base  of  the  tooth  of 


(J)  Transverse  section  across  the  crown  of  tlie  tooth  of  Varanus,  near  to 
its  base.  The  central  pulp  cavity  is  produced  out  into  processes,  and  it 
might  be  said  the  dentine  is  arranged  in  plates  with  some  little  regularity 
round  its  periphery. 

G  2 


84 


A  MANUAL  OF  DENTAL  ANA  TOM Y. 


Lepidosteus  (North  American  bony  pike)  ;  or  sometimes 
there  are  several  branches. 

- 

Fig.  39  0). 


In  Lepidosteus  oxyurus  there  are  simple  inflections,  and 
a  central  pulp  cavity ;  in  L.  spatula  the  inflections  are 
branched,  and  the  central  pulp  cavity  all  filled  up. 

In  the  foregoing  figure  of  the  base  of  a  tooth  of  Lepi¬ 
dosteus  some  few  of  the  outrunning  pulp  chambers  are 

fl)  Transverse  section  across  the  tooth  of  Lepidosteus  spatula.  At  the 
exterior  are  regularly  disposed  radiating  plates  of  dentine,  each  with  its 
own  pulp  cavity,  while  the  central  area  is  composed  of  more  or  less  cylin¬ 
drical  pulp  chambers,  each  of  which  forms  the  starting  point  for  its  own 
system  of  dentinal  tubes.  The  pulp  chambers  are  made  dark  in  the  figure 
for  the  sake  of  greater  distinctness. 


THE  DENTAL  TISSUES. 


85 


seen  to  be  bifurcated,  while  the  central  mass  of  the  tooth 
is  composed  of  dentine  permeated  by  pulp  canals  which 
pursue  a  longitudinal  course  ;  a  slight  further  modification 
brings  us  to  the  structure  of  the  dentine  of  the  Labyrin- 
thodon,  in  which  a  maximum  of  complexity  is  attained, 
although  a  clue  to  its  intimate  structure  is  afforded  by  the 
teeth  of  Yaranus  or  of  Lepidosteus. 


Fig.  40  (J). 


The  laminae  of  pulp,  with  their  several  systems  of  den¬ 
tinal  tubes,  instead  of  passing  out  in  straight  lines  like  the 
spokes  of  a  wheel,  pursue  a  tortuous  course  as  they  run 
from  the  central  small  pulp  chamber  towards  the  surface. 
Not  only  do  they  undulate,  but  they  also  give  off  lateral 

(x)  Transverse  section  of  a  tooth  of  Labyrinthodon.  (After  Owen. ) 

The  latter  a  is  placed  in  the  centre  pulp  chamber ;  the  letter  b  marks 
the  lines  of  separation  between  the  system  of  dentinal  tubes  which  belong 
to  each  lamina  of  pulp  ;  these  lines  of  demarcation  were  formerly  sup¬ 
posed  to  be  occupied  by  cementum. 


86 


A  MANUAL  OF  DENTAL  ANATOMY. 


processes ;  and  at  their  terminations  near  to  the  surface  of 
the  tooth,  the  thin  laminae  of  pulp  (so  thin  that  the  radi¬ 
ating  pulp  chambers  are  mere  fissures)  become  dilated ;  so 
that  on  section  circular  canals  are  seen  at  these  points,  as 
is  also  the  case  at  the  points  where  subsidiary  processes 
branch  off 

Fig.  41  (i). 


The  wavy  course  pursued  by  the  radiating  plates  of  den 
tine,  and  the  disposition  of  the  tubes  round  the  dilated 
portions  of  pulp  chamber,  render  the  general  aspect  of  the 
dentine  structure  very  complicated ;  the  several  “  systems  ”  (2) 

(b  From  tooth  of  Labyrinthodon,  showing  the  nature  of  the  connection 
between  the  contiguous  dentinal  systems.  (After  a  drawing  of  my  father’s.) 

(2)  The  term  “  dentinal  system  ”  is  applied  to  the  portion  of  dentine  in 
which  all  the  tubes  radiate  from  a  single  section  of  pulp  chamber ;  thus 
the  tooth  of  Labyrinthodon  is  made  up  of  many  dentinal  systems ;  the 
same  thing  may  be  said  of  the  tooth  of  Myliobates. 


THE  DENTAL  TISSUES. 


87 


are  united  to  one  another  by  an  inosculation  of  the  terminal 
branches  of  the  tubes  in  some  few  places,  but  more  generally 
by  a  clear  layer  containing  radiate  spaces,  something  like  the 
lacunae  of  cementum.  Hence  Professor  Owen  has  described 
the  tooth  as  consisting  of  radiating  plates  of  dentine,  be¬ 
tween  which  pass  in  equally  convoluted  plates  of  cementum. 
But,  as  was  pointed  out  by  my  father  (Phil.  Trans.  1850),  the 
mere  presence  of  lacuna-like  spaces  is  not  sufficient  to  prove 
the  presence  of  cementum,  inasmuch  as  they  occur  on  a 
small  scale  in  the  granular  layer  of  dentine ;  moreover,  when 
cementum  and  enamel  are  both  present,  the  cementum  is 
always  outside  the  enamel,  whereas  at  the  upper  part  of  the 
tooth  of  the  Labyrinthodon  the  characteristic  inflections  take 
place  within  a  common  investment  of  enamel  which  does 
not  dip  in.  Thus  the  whole  of  the  tissue  constituting  the 
very  complex  pattern  of  the  Labyrinthodon  tooth  is  dentine, 
and  the  cementum  does  not,  as  was  usually  supposed,  enter 
into  its  composition  at  all. 

Another  form  in  which  plici-dentine  may  exist  is  exempli¬ 
fied  in  the  teeth  of  Myliobates,  a  large  Bay ;  or  in  the  teeth 
of  the  rostrum  of  the  saw-fish  (Pristis). 

In  the  Myliobates  (Fig.  42)  the  flat  pavement-like  tooth 
is  permeated  by  a  series  of  equidistant  parallel  straight 
canals,  running  up  at  right  angles  to  the  surface  ;  from  the 
upper  end  and  sides  of  these  channels  systems  of  dentinal 
tubes  radiate,  just  as  the  tubes  radiate  from  the  single  pulp 
chamber  of  a  human  tooth,  save  that  they  run  for  a  com¬ 
paratively  short  distance.  In  transverse  sections  the  tubes 
are  seen  radiating  from  these  channels,  and  at  their  termi¬ 
nations  sometimes  inosculating  with  the  terminal  branches 
of  the  tubes  of  another  system.  The  channels  contain  pro¬ 
longations  of  the  vascular  pulp,  which  are  distinct  in  the 
upper  part  of  the  tooth,  but  intimately  united  together  at 
its  base,  where  the  disposition  of  the  channels  ceases  to  be 
regular,  and,  as  a  consequence,  the  systems  of  dentinal  tubes 


88 


A  MANUAL  OF  DENTAL  ANATOMY. 


pass  from  them  in  various  directions  without  producing  the 
symmetrical  patterns  which  characterise  the  upper  part  of 
the  crown. 

When  the  tooth  comes  into  use  and  its  immediate  surface 


Fig.  42  (1). 


gets  worn  off,  the  ends  of  the  perpendicular  pulp  channels 
would  be  laid  open,  were  it  not  that  they  become  blocked  by 
the  deposition  of  a  transparent  homogeneous  tissue  within 
them,  analogous  to  the  similar  tissue  which  closes  Haversian 
canals  of  an  antler  about  to  be  shed. 

Such  is  an  example  of  plici-dentine  in  a  simple  form,  in 
which  the  tooth  might  be  said  to  be  built  up  of  a  series  of 
small  parallel  denticles;  and  a  similar  structure  is  presented 
by  the  rostral  teeth  of  the  saw-fish,  and  by  the  teeth  of  the 
Orycteropus  or  Cape  ant-eater. 

Vaso-dentine. — In  the  dentine  of  human  teeth  it  occa¬ 
sionally  happens  that  a  larger  canal  is  found,  having  no 
clear  relation  to  the  course  of  the  dentinal  tubes,  which  it 
crosses  at  various  angles ;  this  larger  canal  contained  the 


f1)  Transverse  section  of  the  dentine  of  Myliobates. 


THE  DENTAL  TISSUES. 


89 


blood-vessel,  the  remains  of  which  may  be  found  even  in 
a  dried  section.  But  in  human  dentine  vascular  canals  do 
not  often  occur,  and  when  they  do,  are  to  be  regarded  as 
decided  abnormalities. 

The  accompanying  figure,  representing  a  canal  of  large 

Fig.  43  ('). 


size,  wras  drawn  from  a  specimen  shown  to  me  at  the  Cam¬ 
bridge  (Massachusetts)  Museum  by  Dr.  Andrews. 

In  some  mammalian  teeth  these  vascular  canals  are 
disposed  with  regularity,  running  out  in  loops  from  the  pulp 
cavity,  and  lying,  for  a  considerable  part  of  their  course,  at 
right  angles  to  the  dentinal  tubes. 

In  the  Manatee  for  example  the  dentinal  tubes  radiate 
out  with  i  erfect  regularity  from  the  central  pulp  chamber, 
and,  so  to  speak,  take  no  notice  of  the  vascular  canals, 


(’)  Vascular  canal  in  dentine.  From  a  human  tooth.  „ 


90 


A  MANUAL  OF  DENTAL  ANATOMY. 


which  are  to  be  met  with  (especially  in  the  root)  in  large 
numbers. 

Where  they  are  numerous  the  vascular  canals  form  loops, 
so  as  to  constitute  a  sort  of  plexus  beneath  the  cementum. 

The  Tapir,  whose  teeth  in  external  configuration  are  not 
very  dissimilar  to  those  of  the  Manatee,  also  has  vascular 
canals  in  the  dentine  ;  a  curious  difference  in  this  respect 


Fig.  44  f1). 


was  jDointed  out  by  my  father  (Proc.  Zoolog.  Soc.  1851) 
between  the  Indian  and  the  American  Tapir,  the  former 
having  the  canals  in  the  dentine  of  the  crown  of  the  teeth, 
the  latter  having  them  not.  The  great  extinct  Megatherium 
possessed  dentine  very  rich  in  these  canals  :  to  the  left  of 
the  figure  is  seen  the  inner  portion  of  the  dentine,  rich  in 
them ;  in  the  middle  a  fine  tubed  dentine,  forming  the 
external  layer  of  the  dentine  of  the  whole  tooth,  and  to  the 
right  cementum,  also  rich  in  vascular  tubes. 

In  those  teeth  in  which  the  whole  pulp  is  converted  into 
solid  material,  and  no  pulp  cavity  remains,  the  last  portions 
of  the  pulp  are  often  converted  into  dentine  which  has  not 
the  same  character  as  that  of  the  rest  of  the  tooth.  Thus 

0)  Dentine  and  cementum  of  Megatherium  ;  the  latter  to  the  right  of 
the  figure.  >  .  .  .  ’  '  ; 


THE  DENTAL  TISSUES . 


91 


in  teeth  of  perpetual  growth,  such  as  the  incisors  of  rodents, 
the  axial  portion  of  the  tooth  is  that  latest  calcified,  and 
consists  of  a  dentine  containing  vascular  canals,  which  are 
not  present  in  the  other  part  of  the  tooth.  When  a  change 
thus  occurs  in  the  character  of  the  tissue  formed  at  a  later 
time  than  the  rest  of  the  dentine,  the  name  “secondary 
dentine  ”  is  applied  to  the  resultant  tissue. 

But  secondary  dentine  may  partake  of  several  different 
varieties  of  structure,  so  that  the  term  must  not  he  taken  as 

Fio.  45  f1). 


denoting  anything  more  than  the  circumstances  under  which 
it  was  formed. 

It  is  in  the  class  of  Fish,  in  which  vaso-dentine  is  rather 
common,  that  the  most  instructive  examples  of  its  nature 
are  to  be  found. 

The  conical  teeth  of  the  common  Flounder,  and  indeed  of 
most  flat  fish  (Pleuronectidse)  have  their  pointed  tips  formed 

(!)  Tooth  of  a  Flounder,  a,  Dentinal  tubes  near  apex  of  tooth  ;  b, 
Vascular  canals  ;  c,  Spear  points  of  enamel. 


92 


A  MANUAL  OF  DENTAL  ANATOMY. 


of  ordinary  hard  dentine,  surmounted  by  enamel  tips.  In 
this  part  of  the  tooth  the  dentinal  tubes  are  numerous,  and 
regular  in  their  disposition,  radiating  out  from  the  axial  pulp 
chamber. 

Lower  down  in  the  teeth  the  dentinal  tubes  become  less 
numerous,  and  at  the  same  time  much  larger  looped  canals 
make  their  appearance,  and  as  these  become  more  numerous 


Fig.  46  (*). 


c 


and  regular  so  do  the  dentinal  tubes  become  less  so.  These 
larger  tubes  contain  blood-vessels,  and  red  blood  circulates 
through  them  during  the  life  of  the  tooth. 

We  may  suppose  that  the  nutrition  of  the  dentine  maybe 
provided  for  either  by  protoplasm  carried  for  a  long  distance 
from  the  pulp  by  the  dentinal  tubes,  or  by  blood  circulating 
through  the  larger  vascular  channels,  but  that  both  are  not 
required,  and  so  do  not  exist  together. 

And  whilst  the  teeth  of  the  Manatee,  the  Tapir,  and  of 

(J)  Tooth  of  Ostracion.  a,  Enamel  ;  b,  Capillary  channels  ;  c,  Axial 
pulp  chamber. 


THE  DENTAL  TISSUES. 


93 


the  Flounder  teach  that  hard  dentine  and  vaso-dentine  are 
not  very  dissimilar  in  their  nature,  and  that  the  one  passes 
by  imperceptible  gradations  into  the  other,  the  dentine  at  the 
base  of  the  Flounder’s  tooth  provides  us  with  an  example  of 
typical  vaso-dentine :  that  is  to  say,  dentine  in  which  the 
dentinal  tubes  are  quite  absent,  having  had  their  place 
taken  by  a  complete  system  of  vascular  channels. 

The  teeth  of  the  Ostracion  (Fig.  46),  or  of  the  Hake  (Figs. 
47  and  89),  afford  good  examples  of  this  form  of  tissue. 

Fig.  47  (l). 


The  matrix  is  solid,  so  far  as  penetration  by  fine  tubes 
goes,  but  it  contains  a  system  of  larger  canals  which  carry 
only  blood,  and  no  pulp  tissue,  out  to  near  the  surface  of 
the  dentine,  where  they  form  a  plexus. 

I  have  not  been  able  to  satisfy  myself  of  the  existence  of 
any  definite  structure  in  the  matrix  ;  sometimes  it  looks 
granular,  and  sometimes  has  a  finely  reticulated  look,  re¬ 
calling  the  appearances  described  by  Bodecker  in  human 
dentine.  (See  page  74.) 

(!)  Section  of  Dentine  from  a  freslily  caught  Hake  (Merlucius).  d, 
Dentine  matrix  ;  cp,  Capillary  blood-vessels  banging  out  from  its  edge, 
containing  here  and  there  abundant  blood-corpuscles. 


94 


A  MANUAL  OF  DENTAL  ANATOMY. 


The  arrangement  of  the  vascular  canals  is  regular  and 
striking,  reminding  one  of  the  appearance  of  the  capillary 
network  in  an  injected  intestinal  villus.  In  fact,  an  intes¬ 
tinal  villus  petrified,  whilst  the  capillary  network  remained 
pervious  and  carried  red  blood  circulating  through  it,  would 
form  no  bad  representation  of  a  conical  vaso-dentine  tooth. 

For  these  canals  do  actually  contain  capillaries,  and  blood 
actively  circulates  through  them  ;  a  section  cut  from  the 
fresh,  brilliantly  red  tooth  of  a  Hake  often  shows  the  coats 
of  the  capillary  hanging  out  from  the  edge,  and  the  canals 
full  of  blood  corpuscles  (Fig.  47). 

In  all  vaso-dentine  teeth  with  which  I  am  acquainted  the 
pulp  chamber  is  of  simple  form,  the  pulp  coated  by  a  distinct 
layer  of  odontoblasts,  and  no  pulp  tissue  other  than  the 
capillaries  passing  out  into  the  dentine,  so  that  each  capil¬ 
lary  fits  and  wholly  fills  its  channel  in  the  dentine. 

Vaso-dentine  is  less  dense  and  hard  than  ordinary  dentine, 
and  consequently  generally  gets  protection  by  a  harder  tissue 
when  exposed  to  hard  work. 

The  teeth  of  the  Hake,  used  simply  for  piercing  and 
catching  fish,  are  merely  tipped  with  enamel  (Fig.  89) ; 
those  of  Ostracion,  put  to  severer  work,  are  coated  with 
enamel,  while  the  teeth  of  the  Wrasse  (Labrus),  which  are 
composed  of  ordinary  dentine  are,  though  very  hard  worked, 
unprotected  by  enamel. 

Osteo-dentine, — This  is  a  tissue  far  more  sharply  marked 
off  from  hard  dentine,  plici-dentine  and  vaso-dentine,  than 
these  are  from  one  another,  and  approaches  closely  to  bone, 
from  which  it  has  few  points  of  essential  difference. 

The  distinction  can  hardly  be  fully  emphasized  until  the 
development  of  dentine  has  been  described,  but  it  may  be 
mentioned  that  it  is  not  developed  entirely  upon  the  surface 
of  the  pulp,  from  an  odontoblast  layer,  but  within  its  whole 
substance.  Consequently  in  a  completed  osteo-dentine  tooth 
there  is  no  single  simple  pulp,  which  can  be  withdrawn  from 


THE  DENTAL  TISSUES. 


95 


the  tooth,  but  pulp  and  calcified  tissue  are  quite  inextricably 
mixed  up. 

Fig.  48  (J). 


And  though  there  are  numerous  large  channels,  often 
muclr  larger  than  those  of  vaso-dentine,  they  are  less  regular, 
do  not  in  their  arrangement  suggest  the  idea  of  capillary 
loops,  and  in  a  fresh  tooth  contain  masses  of  pulp-structure 
as  well  as  blood-vessels. 

The  Pike’s  tooth  affords  a  good  example  of  osteo-dentine. 
Its  surface  is  formed  of  a  layer  of  fine  tubed  tissue,  almost 

f1)  Tooth  of  Common  Fike.  a,  Outer  layer  of  fine  tubed  dentine  ;  b, 
inner  mass  of  osteo-dentine. 


96 


A  MANUAL  OF  DENTAL  ANATOMY . 


like  ordinary  dentine,  but  this  soon  gives  place  to  a  coarsely 
channeled  tissue,  containing  elongated  spaces  filled  with 
pulp,  from  which  canaliculi,  like  those  of  a  bone  lacuna, 
branch  off  in  all  directions,  but  do  not  run  far. 

Very  many  sharks  have  teeth  composed  of  osteo-dentine, 


Fro.  49  P). 


with  an  outer  dense  layer  :  the  tooth  of  Lamna  here  figured 
shows  a  central  core  of  osteo-dentine,  which  constitutes  the 
bulk  of  the  tooth  ;  external  to  this  a  somewhat  thin  layer  of 
hard  dentine,  in  which  all  the  dentinal  tubes  run  out  at 
right  angles  to  the  surface,  but  are  derived  from  the  channels 
of  the  osteo  -dentine  and  not  from  any  single  pulp  chamber ; 
while  the  outermost  layer,  which  is  clear  and  structureless, 

(i)  Tooth  of  a  species  of  Lamna,  consisting  of  a  central  mass  of  vaso- 
dentine,  passing  towards  its  surface  into  a  fine-tubed  unvascular  dentine. 
The  clear  structureless  layer  on  the  surface  may  probably  be  regarded  as 
enamel. 


THE  DENTAL  TISSUES. 


97 


may  be  merely  the  outer  part  of  the  hard  dentine,  or  may 
be  a  thin  layer  of  enamel.  It  is  to  be  regretted  that  special 
names  have  been  given  to  this  layer ;  it  is  sometimes  called 
vitro-dentine,  sometimes  ganoin  or  fish-enamel  ;  but  there  is 
no  reason  why  it  should  have  a  special  name  at  all.  The 
similarity  of  the  channels  of  pulp  in  osteo-dentine  to  Haver¬ 
sian  canals  in  bone  is  very  close ;  in  fact,  when  teeth 
consisting  of  osteo-dentine  become,  as  in  many  fish  they 
do,  anchylosed  to  the  subjacent  bone,  it  becomes  impos¬ 
sible  to  say  at  what  point  the  dentine  ends  and  the  bone 
commences  ;  and  this  difficulty  is  intensified  by  the  fact  that 
the  bone  of  many  fishes  lacks  lacunae,  and  is  almost  exactly 
like  dentine. 

Osteo-dentine  was  defined  by  Professor  Owen  as  dentine 
in  which  the  matrix  was  arranged  in  concentric  rings  around 
the  vascular  canals,  and  in  which  lacunae  similar  to  those  of 
bone  were  found. 

But  neither  of  these  characters  are  to  be  found  in  many 
teeth,  which,  if  the  manner  of  their  development  is  to  be 
taken  into  account,  are  unquestionably  made  of  osteo-den¬ 
tine  ;  and  so  they  cannot  be  made  use  of  for  purposes  of 
definition,  although  lacunae  and  lamination  of  the  matrix 
are  far  more  often  present  in  osteo-dentine  than  in  the  other 
varieties  of  dentinal  structure. 

The  varieties  of  dentine  may  be  grouped  thus  : — 

(A.)  Dentines  developed  upon  the  surface  of  a  pulp,  by 
calcification  of  a  specialised  layer  of  odontoblast 
cells. 

(i.)  Hard,  un vascular  dentine,  thoroughly  per¬ 
meated  with  dentinal  tubes,  which  radiate 
from  a  simple  central  pulp  chamber. 
Example — Hum  an  dent  ine. 

(ii.)  Plici-dentine,  permeated  with  dentinal 
tubes,  which  radiate  from  a  pulp  chamber 


ii 


98 


A  MANUAL  OF  DENTAL  ANATOMY 


rendered  complex  in  form  by  foldings  in 
of  its  walls.  Example — Lepidosteus, 
Labvrinthodon. 

(iii.)  Yaso-dentine,  dentinal  tubes  few  or 
absent,  but  capillary  channels  with 
blood  circulating  through  them  abun¬ 
dant.  Example — Hake. 

(B.)  Dentines  developed  by  calcification  shooting 
through  the  interior  of  a  pulp,  not  by  calcifi¬ 
cation  of  a  specialised  surface  layer  of  cells. 

(iv.)  Osteo-dentine;  with  no  long  dentinal 
tubes,  but  minute  tubes  analogous  to 
bone  canaliculi,  and  large  irregular 
channels  containing  pulp-tissue  (not 
blood-vessels  only).  Example — Pike. 

It  remains  to  be  added  that  the  same  pulp  may  undergo 
a  change  in  the  manner  of  its  calcification ;  that  is  to  say, 
that  after  having  gone  on  with  surface  calcification  from 
an  odontoblast  layer  for  a  certain  length  of  time,  this  may 
give  place  to  a  more  irregular  internal  calcification  into  an 
osteo-dentine. 

This  is  especially  prone  to  happen  after  injury,  and  is 
often  exemplified  upon  a  large  scale  in  Elephants’  tusks  ; 
the  pulp  of  which,  normally  engaged  in  calcifying  the 
odontoblast  layers  into  ivory,  may  after  an  injury  calcify 
irregularly,  and  solidify  into  a  coarse  osteo-dentine. 

It  will  then  be  easy  to  understand  that  so-called  secon¬ 
dary  dentine,  produced  in  a  pulp  which  ordinarily  forms 
hard  dentine,  may  partake  of  the  character  of  vaso-  or  of 
osteo-dentine. 

Thus  the  pulp  of  a  sperm  whale’s  tooth  becomes  oblite¬ 
rated  by  a  development  of  secondary  dentine,  which  some¬ 
times  forms  irregular  masses  loose  in  the  pulp  chamber,  and 
sometimes  is  adherent  to  and  continuous  with  the  dentine 


THE  DENTAL  TISSUES. 


93 


previously  formed.  The  structure  of  these  masses  is  very 
confused.  Tubes,  of  about  the  same  diameter  as  dentinal 
tubes,  abound  ;  but  they  are  often  arranged  in  tufts  or  in 
bundles,  and  without  any  apparent  reference  to  any  com 


Fig.  50  (l). 


mon  points  of  radiation.  Irregular  spaces,  partaking  of  the 
character  of  interglobular  spaces  or  of  bone  lacuna?,  abound; 
and  vascular  canals  are  also  common. 

In  the  human  tooth  secondary  dentine  occurs  in  the  teeth 
of  aged  persons,  in  which  the  pulp  cavity  is  much  contracted 
in  size,  and  is  also  very  frequently  formed  as  a  protection  to 
the  pulp  when  threatened  by  the  approach  of  dental  caries, 
or  by  the  thinning  of  the  walls  of  the  pulp  cavity  through 
■excessive  wear.  The  following  figure,  representing  one 
of  the  cornua  of  the  pulp  chamber  from  a  molar  tooth 
affected  by  caries,  is  a  good  example  of  secondary  dentine 

(x)  Section  of  a  mass  of  secondary  dentine  from  the  tooth  of  a  sperm 

whale. 


100 


A  MANUAL  OF  DENTAL  ANATOMY. 


It  occasionally  happens  that  the  pulp  resumes  its  formative 
activity,  and  new  dentine  is  developed  which,  with  the 
exception  of  a  slight  break  or  bend  in  the  continuity  of  the 
tubes,  is  almost  exactly  like  normal  dentine.  More  often,, 

Fig.  51  (*). 


however,  the  boundary  line  between  the  old  and  the  new  is 
marked  by  an  abundance  of  irregular  spaces  and  globular 
contours,  whilst  further  in  the  mass  of  new  secondary  dentine, 
the  tubular  structure  again  asserts  itself  more  strongly  ; 
this  is  well  seen  in  the  specimen  figured. 


THE  TOOTH  PULP. 

The  pulp  occupying  the  central  chamber  or  pulp  cavity, 
was  the  formative  organ  of  the  tooth,  and  consequently  varies 

(b  Secondary  dentine  filling  up  one  of  tlie  cornua  of  the  pulp  cavity. 
From  a  human  molar  affected  by  caries. 


THE  DENTAL  TISSUES. 


101 


in  its  anatomical  characters  according  to  its  age.  As  well  as 
being  what  remains  of  a  formative  organ,  it  is  the  source  of 
Vascular  and  nervous  supply  to  the  dentine. 

The  pulp  may  be  described  as  being  made  up  of  a  mucoid 
gelatinous  matrix,  containing  cells  in  abundance,  which  arc 
especially  numerous  near  to  its  periphery.  In  it  some 
fibrous  connective  tissue  is  discoverable,  though  this  is  not 
Abundant  until  the  period  of  degeneration  has  set  in.  Nerves 
nnd  vessels  also  ramify  abundantly  in  it. 

The  matrix  substance  remaining  in  large  proportion, 
•whilst  the  cell  elements  are  not  greatly  developed,  and  the 
fibrous  element  being  still  less  conspicuous,  gives  to  the 
pulp  the  character  common  to  many  embryonal  tissues. 

In  some  specimens  prepared  by  Mr.  Mummery,  in  which 
the  pulp  in  situ  is  impregnated  with  hardened  balsam,  and 
the  whole  cut  and  rubbed  down  subsequently,  there  is  an 
appearance  as  though  the  matrix  substance  against  the 
dentine  had  a  sort  of  fenestrated  structure,  and  as  if  bands 
of  it  ran  into  the  dentine  (cf.  Sharpey’s  fibres  in  ce- 
mentum). 

I  had  myself  observed  some  indication  of  a  similar 
appearance  in  pulps  which  had  been  differently  treated,  yet 
it  is  by  no  means  certain  how  far  it  is  due  to  method  of 
preparation,  nor  whether  this  may  not  be  half  formed 
dentine  which  takes  on  this  appearance. 

The  cellidar  elements  of  the  pulp  are  arranged,  as  seen 
in  transverse  sections,  in  a  direction  radiating  outwards  from 
the  centre ;  this  is  most  marked  in  the  highly  specialised 
layer  of  cells  which  form  the  surface  of  the  pulp,  and  arc 
termed  odontoblasts. 

The  odontoblast  layer,  sometimes  called  the  membrana 
tboris,  because  it  usually  adheres  more  strongly  to  the 
dentine  than  to  the  rest  of  the  pulp,  and  is  therefore  often 
left  behind  upon  the  dentine  when  the  pulp  is  torn  away, 
consists  of  a  single  row  of  large  elongated  cells,  of  darkish 


102 


A  MANUAL  OF  DENTAL  ANATOMY. 


granular  appearance,  with  a  large  and  conspicuous  nucleus 
near  to  the  end  farthest  from  the  dentine. 

The  sharp  contours  which  the  odontoblasts  possess  in 
pulps  which  have  been  acted  on  by  chromic  acid,  alcohol, 
or  even  water,  are  absent  in  the  perfectly  fresh  and  unaltered 
condition,  and  it  is  believed  that  they  have  no  special  in¬ 
vesting  membrane.  They  are  furnished  with  three  sets  of 
processes.  The  dentinal  process  (which  is  equivalent  to  the 
dentinal  fibre)  enters  the  canal  in  the  dentine,  and  the  in¬ 
dividual  odontoblast  may  be  furnished  with  several  dentinal 
processes.  By  means  of  lateral  processes  the  cells  communi¬ 
cate  with  those  on  either  side  of  them,  and  by  means  of 
their  pulp  processes  with  cells  lying  more  deeply ;  these 
deeper  cells  again  are  to  some  extent  intermediate  in  size 
between  the  odontoblasts  and  the  internal  cells  of  the  pulp. 
The  membrana  eboris  covers  the  surface  of  the  pulp  like 
an  epithelium.  The  odontoblasts  vary  much  in  form  at 
different  periods ;  in  the  youngest  pulps,  prior  to  the  forma¬ 
tion  of  dentine,  they  are  roundish,  or  rather  pyriform ; 
during  the  period  of  their  greatest  functional  activity  the 
end  directed  towards  the  dentine  is  squarish,  though  tapering 
to  a  slight  extent  into  the  dentinal  process  ;  while  in  old 
age  they  become  comparatively  inconspicuous,  and  assume 
a  rounded  or  ovoid  shape.  The  general  matrix  of  the  pulp, 
as  has  been  before  noted,  is  of  firm,  gelatinous  consistency ; 
it  is  a  little  more  dense  upon  the  surface,  whence  has 
perhaps  arisen  the  erroneous  idea  that  the  pulp  is  bounded 
by  a  definite  membrane. 

The  vessels  of  the  pulp  are  very  numerous ;  three  or 
more  arteries  enter  at  the  apical  foramen,  and  breaking  up 
into  branches  which  are  at  first  parallel  with  the  long  axis 
of  the  pulp,  finally  form  a  capillary  plexus  immediately 
beneath  the  cells  of  the  membrana  eboris. 

No  lymphatics  are  known  to  occur  in  the  tooth  pulp. 

The  nerves  enter  usually  by  one  largish  trunk  and  three 


THE  DENTAL  TISSUES. 


103 


or  four  minute  ones  :  after  pursuing  a  parallel  course,  and 
giving  oft*  some  branches  which  anastomose  but  little,  in  the 
expanded  portion  of  the  pulp  they  form  a  rich  plexus  beneath 
the  membrana  eboris,  as  has  been  described  by  Raschkow 
and  many  subsequent  writers. 

But  here  our  exact  knowledge  ends,  for  the  nature  of  the 
terminations  of  the  nerve  fibres  in  the  pulp  is  not  with 
certainty  known :  the  primitive  fibrils,  which  are  extra¬ 
ordinarily  abundant  near  to  the  surface  of  the  pulp,  often 
form  meshes,  but  this  does  not  appear  to  be  their  real 
termination. 

Boll,  as  has  been  mentioned  at  a  previous  page,  investi¬ 
gated  this  point,  and  found  that  if  a  pulp  be  treated  for  an 
hour  with  very  dilute  chromic  acid  solution,  an  immense 
number  of  fine  non-medullated  nerve  fibres,  which  he  suc¬ 
ceeded  in  tracing  into  continuity  with  the  larger  medullated 
fibres,  may  be  discerned  near  to  the  surface  of  the  pulp. 
The  ultimate  destination  of  these  nerve  fibres  is  un¬ 
certain  ;  but  he  has  seen  them  passing  through  the  mem. 
brana  eboris,  and  taking  a  direction  parallel  to  that  of  the 
dentinal  fibrils  in  such  numbers  that  he  infers  that  they 
have  been  pulled  out  from  the  canals  of  the  dentine.  Still, 
whatever  may  be  the  probabilities  of  the  case,  he  has  not 
seen  a  nerve  fibre  definitely  to  pass  into  a  dentinal  canal, 
nor  has  any  other  observer  been  more  fortunate. 

Boll’s  observations  have  not  however  been  fully  confirmed 
by  any  subsequent  worker  in  the  field,  nor  had  they  been 
definitely  controverted  until  Magitot  recently  stated  that  he 
had  fully  satisfied  himself  that  the  nerves  become  continuous 
with  the  branched  somewhat  stellate  cells  which  form  a  layer 
beneath  the  odontoblasts,  and  through  the  medium  of  these 
cells  with  the  odontoblasts  themselves.  (See  Fig.  33.) 

If  this  view  of  their  relation  to  the  nerves  be  correct  the 
sensitiveness  of  the  dentine  would  be  fully  accounted  for 
without  the  necessity  for  the  supposition  that  actual  nerve 


104 


A  MANUAL  OF  DENTAL  ANATOMY. 


fibres  enter  it,  for  the  dentinal  fibrils  would  be  in  a 
measure  themselves  prolongations  of  the  nerves. 

It  has  already  been  mentioned  that  the  pulp  undergoes 
alterations  in  advanced  age,  its  diminution  in  size  by  its 
progressive  calcification  and  the  addition  thus  made  to  the 
walls  of  the  pulp  cavity  being  the  most  conspicuous  change 
which  occurs.  In  pulps  which  have  undergone  a  little 
further  degeneration,  the  odontoblast  layer  becomes  atro¬ 
phied  ;  fibrillar  connective  tissue  becomes  more  abundant, 
coincidently  with  the  diminution  in  the  quantity  of  the  cel¬ 
lular  elements.  Finally,  the  capillary  system  becomes 
obliterated  by  the  occurrence  of  thrombosis  in  the  larger 
vessels,  the  nerves  undergo  fatty  degeneration,  and  the  pulp 
becomes  reduced  to  a  shrivelled,  unvascular,  insensitive 
mass.  These  changes  may  go  on  without  leading  to  actual 
putrefactive  decomposition  of  the  pulp,  and  are  hence  not 
attended  by  alveolar  abscess ;  but  a  tooth  in  which  the  pulp 
has  undergone  senile  atrophy  is  seldom  fast  in  its  socket. 

The  pulps  of  the  teeth  of  some  animals  become  eventually 
entirely  converted  into  secondary  dentine,  but  it  would  seem 
to  be  very  generally  the  case  that  those  teeth  which  exercise 
very  active  functions  and  last  throughout  the  life  of  the 
creature  retain  their  pulp  in  an  active  and  vascular  condition. 


CEMENTUM. 

The  cement  forms  a  coating  of  variable  thickness  over 
the  roots  of  the  teeth,  sometimes,  when  the  several  roots  arc 
very  close  to  another,  or  the  cement  is  thickened  by  disease, 
uniting  the  several  roots  into  one. 

The  cement  is  ordinarily  said  to  be  absent  from  the 
crowns  of  the  teeth  of  man,  the  carnivora,  &c.,  and  to  com¬ 
mence  by  a  thin  edge  just  at  the  neck  of  the  tooth,  over¬ 
lapping  the  enamel  to  a  slight  extent ;  it  is,  in  the  healthy 
state,  thickest  in  the  interspaces  between  the  roots  of  molar 


THE  DENTAL  TISSUES. 


105 


or  bicuspid  teeth  :  it  is,  however,  often  thickened  at  the  end 
of  a  root  by  a  dental  exostosis.  In  compound  teeth,  the 
cementum  forms  the  connecting  substance  between  the  den¬ 
ticles  (see  the  figures  of  the  tooth  of  the  Capybara,  the 
Elephant,  <fec.),  and,  before  the  tooth  has  been  subject  to 
wear,  forms  a  complete  investment  over  the  top  of  the 
crown.  The  cementum  also  covers  the  crowns  of  the  com¬ 
plex-patterned  crowns  of  the  teeth  of  ruminants  ;  and,  in 


Fig.  52  (*). 


my  opinion,  is  present  in  a  rudimentary  condition  upon  the 
teeth  of  man,  &c.,  as  Nasmyth’s  membrane.  The  cementum 
is  the  most  external  of  the  dental  tissues  :  a  fact  which 
necessarily  follows  from  its  being  derived  more  or  less  directly 
from  the  tooth  follicle. 

Both  physically  and  chemically,  and  also  in  respect  of  the 
manner  of  its  development,  the  cementum  is  closely  allied 
to  bone.  It  consists  of  a  laminated  calcified  matrix  or  basal 
substance,  and  lacunae.  Vascular  canals  corresponding  to 


(b  Thick  laminated  cementum  from  the  root  of  a  human  tooth. 


106 


A  MANUAL  OF  DENTAL  ANATOMY. 


the  Haversian  canals  of  bone,  are  met  with,  but  it  is  only  in 
thick  cementum  that  they  exist  ;  and,  in  man,  perhaps  in 
exostosis  more  often  than  in  the  thick  healthy  tissue. 

The  lamellae  of  the  cementum  are  thinner  towards  the 
neck  of  the  tooth,  being  thickest  at  the  apex  of  the  root,  but 
the  number  of  the  lamellae  is  about  the  same  in  all  parts  of 
the  tooth. 

Soon  after  the  completion  of  a  tooth,  there  are  but  few 
lamellae,  and  an  adult  has  cementum  far  thicker  than  a 


Fig.  53  0). 


child  ;  an  aged  person  again  having  more  than  an  adult.  Very 
possibly  it  is  to  be  regarded  as  growing  at  intervals  through 
the  life  of  the  individual  (Black). 

The  matrix  is  a  calcified  substance,  which,  when  boiled 
yields  gelatine,  and  if  decalcified  retains  its  form  and  struc¬ 
ture  :  it  is,  in  fact,  practically  identical  with  the  matrix  of 
bone.  It  is  sometimes  apparently  structureless,  at  others 
finely  granular,  or  interspersed  with  small  globules. 

The  lacunae  of  cementum  share  with  those  of  bone  the 
following  characters  :  in  dried  sections  they  are  irregular 
cavities,  elongated  in  the  direction  of  the  lamellae  of  the 
matrix,  and  furnished  with  a  large  number  of  processes. 
The  processes  of  the  lacunae  (known  as  canaliculi)  are  most 

i1)  Lacuna  of  cementum  wliicli  communicates  with  the  terminations  of 
the  dentinal  tubes. 


THE  DENTAL  TISSUES. 


107 


abundantly  given  oft’  at  right  angles  to  the  lamellae  (see 
Fig.  52),  and,  again,  in  cementum,  are  more  abundantly 
directed  towards  the  exterior  of  the  root  than  towards  the 
dentine.  The  lacunae  of  cementum  differ  from  those  of 
bone  in  being  far  more  variable  in  size,  in  form,  and  in  the 
excessive  number  and  length  of  their  canaliculi ;  in  this 
latter  respect  the  lacunae  of  the  cement  of  Cetacean  teeth 
are  very  remarkable. 

Many  of  the  lacunae  in  cementum  are  connected,  by  means 
of  their  canaliculi,  with  the  terminations  of  the  dentinal 
tubes  (Fig.  53)  ;  they,  by  the  same  means,  freely  intercom¬ 
municate  with  one  another,  while  others  of  their  processes 
are  directed  towards  the  surface,  which,  however,  in  most 
instances,  they  do  not  appear  to  actually  reach. 

The  lacunae  assume  all  sorts  of  peculiar  forms,  especially 
in  the  thicker  portion  of  the  cement. 

Here  and  there  lacunae  are  to  be  found  which  are  fur¬ 
nished  with  comparatively  short  processes,  and  are  contained 
within  well-defined  contours.  Sometimes  such  a  line  is  to 
be  seen  surrounding  a  single  lacuna,  sometimes  several 
lacunae  are  enclosed  within  it ;  lacunae  so  circumscribed  are 
called  “  encapsuled  lacunae,”  and  were  first  observed  by 
Gerber  in  the  cement  of  the  teeth  of  the  horse  (they  are 
specially  abundant  in  the  teeth  of  the  solidungulata).  By 
cautious  disintegration  of  the  cementum  in  acids  these  eir 
capsuled  lacunae  may  be  isolated  ;  the  immediate  walls  of 
the  lacunae  and  canaliculi,  just  as  in  bone,  being  composed 
of  a  material  which  has  more  power  of  resisting  chemical 
re-agents  than  the  rest  of  the  matrix. 

The  encapsuled  lacunae  are  to  be  regarded  as  individual 
osteoblasts,  or  nests  of  osteoblasts,  which  have  to  some 
extent  preserved  their  individuality  during  calcification. 

In  the  fresh  condition  it  ajDpears  probable  that  the  lacunae 
are  filled  up  by  soft  matrix,  which  shrinks  up,  and  so  leaves 
them  as  cavities  in  dried  sections.  It  can  hardly  as  yet  be 


108 


A  MANUAL  OF  DENTAL  ANATOMY. 


said  that  the  question  of  the  contents  of  lacunae  has  been 
finally  settled,  though  the  researches  of  Bodecker  and  Heitz- 
mann  have  gone  far  towards  doing  so. 

According  to  them  each  lacuna  contains  a  protoplasmic 
body,  which  they  term  the  cement  corpuscle,  with  a  central 
nucleus. 

This  nucleus  may  be  large  and  surrounded  by  but  little 
protoplasm,  or  it  may  be  small ;  or  there  may  be  many 
nuclei. 

The  cement  corpuscles  communicate  freely  with  one  another 
by  offshoots,  those  of  large  size  occupying  the  conspicuously 
visible  canaliculi  of  the  lacunse,  whilst  the  finer  offshoots  are 
believed  by  them  to  form  a  delicate  network  through  the 
whole  basis  substance  or  matrix.  The  cement  corpuscles  near 
to  the  external  surface  give  off  numerous  offshoots  which 
communicate  with  protoplasmic  bodies  in  the  periosteum. 
By  this  means  the  cementum  can  remain  alive  even  when 
the  pulp  of  the  tooth  is  dead,  and  thus  the  tooth  be  in  no 
way  a  mere  foreign  body,  dead  and  inert. 

Like  bone,  cementum  contains  Sharpey’s  fibres ;  that  is  to 
say,  rods  running  through  it  at  right  angles  to  its  own 
lamination,  and,  as  it  were,  perforating  it.  These  are  pro¬ 
bably  calcified  bundles  of  connective  tissue.  And  it  is  by 
the  medium  of  these  that  the  alveolo-dental  periosteum 
adheres  to  the  cementum. 

Where  the  cementum  is  very  thin,  as,  for  instance,  where 
it  commences  at  the  neck  of  a  human  tooth,  it  is  to  all 
appearance  structureless,  and  does  not  contain  any  lacuna?, 
and  therefore  no  protoplasmic  bodies  :  nevertheless  lacuna? 
may  be  sometimes  found  in  thin  cementum,  as,  for  example, 
in  that  thin  la}Tcr  which  invests  the  front  of  the  enamel  Gf 
the  rodent-like  tooth  of  a  wombat. 

The  cementum  at  the  neck  is  also  devoid  of  lamellae  ;  it 
appears  to  be  built  up  by  direct  ossification  of  osteoblasts, 
the  prismatic  shape  of  which  may  be  traced  in  it :  Bodecker 


THE  DENTAL  TISSUES. 


109 


describes  it  as  permeated  by  a  fine  but  abundant  network 
of  soft  living  matter.  The  larger  dentinal  tubes  fall  short 
of  the  boundary  line  at  the  neck,  but  a  fine  protoplasmic 
network  crosses  it.  Bodecker  states  that  it  has  a  covering 
of  epithelial  elements,  like  those  of  the  gum. 

The  outermost  layer  of  thick  cementum  is  a  glassy  film, 
denser  apparently  than  the  subjacent  portions,  and  quite 
devoid  of  lacuna) ;  on  the  surface  it  is  slightly  nodular,  and 
might  be  described  as  built  up  of  an  infinite  number  of 
very  minute  and  perfectly  fused  globules ;  this  is,  in  fact, 
the  youngest  layer  of  cement,  and  is  closely  similar  to  that 
globular  formation  which  characterizes  dentine  at  an  early 
stage  of  its  development. 

The  cementum  is  very  closely,  indeed  inseparably,  con¬ 
nected  with  the  dentine,  through  the  medium  of  the 
“  granular”  layer  of  the  latter  ;  the  fusion  of  the  two  tissues 
being  so  intimate,  that  it  is  often  difficult  to  say  precisely 
at  what  point  the  one  may  be  said  to  have  merged  into  the 
other.  And  in  this  region  there  is  an  abundant  passage  of 
protoplasmic  filaments  across  from  the  one  to  the  other. 

Nasmyth’s  membrane. — Under  the  names  of  Nasmyth’s 
membrane,  enamel  cuticle,  or  persistent  dental  capsule,  a 
structure  is  described  about  wrhich  much  difference  of 
opinion  has  been,  and  indeed  still  is,  expressed.  Over  the 
enamel  of  the  crown  of  a  human  or  other  mammalian  tooth, 
the  crown  of  which  is  not  coated  by  a  thick  layer  of  cemen¬ 
tum,  there  is  an  exceedingly  thin  membrane,  the  existence 
of  which  can  only  be  demonstrated  by  the  use  of  acids, 
which  cause  it  to  become  detached  from  the  surface  of  the 
enamel.  When  thus  isolated  it  is  found  to  form  a  continu¬ 
ous  transparent  sheet,  upon  which,  by  staining  with  nitrate 
of  silver,  a  reticulated  pattern  may  be  brought  out,  as 
though  it  were  made  up  of  epithelial  eells.  The  inner 
surface  of  Nasmyth’s  membrane,  is,  however,  pitted  for  the 
reception  of  the  ends  of  the  enamel  prisms,  which  may  have 


110 


A  MANUAL  OF  DENTAL  ANATOMY. 


something  to  do  with  this  reticulate  appearance.  It  is 
exceedingly  thin,  Ivolliker  attributing  to  it  a  thickness  of 
only  one  twenty-thousandth  of  an  inch,  but,  nevertheless, 
it  is  very  indestructible,  resisting  the  action  of  strong  nitric 
or  hydrochloric  acid,  and  only  swelling  slightly  when  boiled 
in  caustic  potash.  Notwithstanding,  however,  that  it  resists 
the  action  of  chemicals,  it  is  not  so  hard  as  the  enamel,  and 


Fig.  54  p). 


becomes  worn  off  tolerably  speedily,  so  that  to  see  it  well  a 
young  and  unworn  tooth  should  be  selected. 

Observations  upon  the  presence  or  absence  of  Nasmyth’s 
membrane  in  fish  and  reptiles  are  very  much  needed  ;  my 
own  recent  investigations  upon  the  development  of  the 
teeth  in  these  classes  make  me  doubt  whether  the  a  priori 
conclusion  of  Waldeyer,  who  believes  that  the  cuticle  will 
be  found  on  all  teeth,  is  not  based  upon  an  interpretation  of 
its  nature  which  is  incorrect. 

The  observation  of  Professor  Huxley,  who  believed  that 

P)  From  a  section  of  a  bicuspid  tooth  in  which  the  cementmn,  c,  is  con¬ 
tinued  over  the  outside  of  the  enamel,  a  ;  the  dentine  is  indicated  by  the 
letter  b. 


THE  DENTAL  TISSUES. 


Ill 


he  found  it  upon  the  teeth  of  the  frog,  &c.,  may  be  suscep¬ 
tible  of  another  explanation,  to  which  I  shall  have  to  recur, 
merely  premising  here  that  its  presence  is  only  certain  in 
Primates,  Carnivora,  and  Insectivora. 

The  singular  power  of  resistance  to  re-agents  which 
characterises  it  proves  nothing  more  than  that  it  is  a  tissue, 
imperfectly  calcified,  on  the  border-land  of  calcification,  so 
to  speak,  since  similarly  resistant  structures  are  to  be  found 
lining  the  Haversian  canals,  the  dentinal  tubes,  the  surface 
of  developing  enamel,  the  lacunae,  &c. 

In  my  father’s  opinion  (Dental  Surgery,  1859)  it  is  to  be 


Fig.  55  (!). 


regarded  as  a  thin  covering  of  cementum,  and  I  have  given 
additional  evidence  in  support  of  the  view  in  a  paper 
referred  to  already  in  the  list  of  works  which  heads  this 
chapter. 

It  now  and  then  happens  that  the  cementum  upon  a 
more  or  less  abnormal  tooth,  instead  of  ceasing  at  the  neck, 
is  continued  up  over  the  exterior  of  the  enamel.  This 
occurs  less  uncommonly  than  is  generally  imagined,  and 
the  accompanying  figure  represents  a  portion  of  the  crown 
of  such  a  tooth. 


(b  Encapsulecl  lacuna  occupying  a  pit  in  the  enamel. 


112 


A  MANUAL  OF  DENTAL  ANA  TOM  I 


If  the  section  he  made  of  the  grinding  surfaces  of  such 
teeth  as  present  rather  deep  fissures  in  these  situations, 
well  marked  and  unmistakeable  lacunal  cells,  or  encapsuled 
lacunae,  will  be  met  with  writh  considerable  frequency.  Now 
and  then  an  encapsuled  lacuna  may  be  found  occupying  a 


Fig.  56  (b. 


shallow  depression  in  the  enamel  which  it  just  fits,  but 
more  commonly  a  dozen  or  more  are  crowded  together  in  a 
pit  in  the  enamel,  where  they  are  usually  stained  of  a  brownish 
<  colour.  The  occurrence  of  lacunae  in  these  situations  is  far 
from  rare  :  my  father’s  collection  contains  more  than  a  dozen 
good  examples  of  them  in  these  positions. 

Nasmyth’s  membrane,  thin  though  it  is  over  the  exterior 

(b  Nasmyth’s  membrane,  set  free  by  the  partial  solution  of  the  enamel. 
a.  Nasmyth’s  membrane,  b.  Dentine,  d.  Mass  occupying  a  pit  iu  the 
enamel,  e.  Enamel,  ci'.  Torn  end  of  Nasmyth’s  membrane. 


THE  DENTAL  TISSUES. 


113 


of  the  enamel,  is  thickened  when  it  covers  over  a  pit  or 
fissure,  and  when  isolated  by  an  acid  is  seen  to  have  entirely 
filled  up  such  spots.  (Fig.  56.) 

In  these  places,  then,  where  the  encapsuled  lacunae  are  to 
be  found,  Nasmyth’s  membrane  also  exists,  a  fact  which 
alone  would  lend  some  probability  to  the  view  that  it  is 
cementum. 

The  general  absence  of  lacunae  in  Nasmyth’s  membrane 
is  due  to  the  fact  that  it  is  not  thick  enough  to  contain  them  ; 
just  as  the  thinnest  layers  of  unquestionable  cementum  also 
are  without  lacunae. 

In  sections  of  an  unworn  bicuspid  which  was  treated  with 
acid  subsequently  to  its  having  been  ground  thin  and  placed 
upon  the  slide,  I  have  several  times  been  fortunate  enough 
to  get  a  view  of  the  membrane  in  situ  ;  it  then  appears  to 
be  continuous  with  an  exterior  layer  of  cementum,  which 
becomes  a  little  discoloured  by  the  acid  employed  to  detach 
Nasmyth’s  membrane  from  the  enamel.  I  am  therefore 
inclined  to  regard  it  as  young  and  incomplete  cementum, 
and  to  consider  it  as  representing  (upon  the  human  tooth) 
the  thick  cementum  which  covers  the  crowns  of  the  teeth  of 
Herbivora  ;  and  I  am  very  glad  to  learn  from  my  friend 
Dr.  Magitot,  who  has  made  many  as  yet  unpublished  re¬ 
searches  upon  this  subject,  that  he  entirely  concurs  in  this 
view,  which  has  also  the  support  of  Professor  Wedl. 


■< 

The  evidence  offered  that  Nasmyth’s  membrane  is  cementum, 
although  strong,  does  not  amount  to  absolute  proof  ;  it  is  therefore 
desirable  to  briefly  recapitulate  the  other  explanations  of  its  nature 
which  have  been  offered. 

Nasmyth,  who  first  called  attention  to  its  existence,  regarded  it 
as  persistent  dental  capsule  ;  ”  a  view  of  its  nature  not  very  ma¬ 
terially  differing  from  that  advocated  in  these  pages. 

Professor  Huxley  described  it  as  being  identical  with  the  mem- 
brana  performativa  ;  that  is  to  say,  with  a  membrane  which  covered 
the  dentine  papilla  prior  to  the  occurrence  of  calcification,  and 
which  afterwards  came  to  intervene  between  the  formed  enamel 
and  the  enamel  organ.  The  objections  to  the  acceptance  of  this 


I 


114 


A  MANUAL  OF  DENTAL  ANATOMY. 


view  of  its  nature  are  so  inextricably  wrapped  up  with  other  ob¬ 
jections  to  Professor  Huxley’s  theory  of  the  development  of  the 
teeth,  that  they  cannot  profitably  be  detailed  in  this  place  ;  it  will 
suffice  to  say,  that  evidence  and  the  weight  of  authority  alike  point 
to  there  being  no  such  true  membrane  as  this  membrana  performa- 
tiva  in  the  place  in  question. 

Waldeyer  holds  that  it  (i.e.,  Nasmyth’s  membrane)  is  a  product  of 
a  part  of  the  enamel  organ.  After  the  completion  of  the  formation 
of  the  enamel  he  believes  that  the  cells  of  the  external  epithelium 
of  the  enamel  organ  become  applied  to  the  surface  of  the  enamel 
and  there  cornified ;  in  this  way  he  accounts  for  its  resistance  to 
reagents,  and  for  its  peculiar  smell  when  it  is  burnt. 

Its  extreme  thinness,  so  far  as  it  goes,  is  an  objection  to  this 
supposition  :  a  more  weighty  argument  against  it  is  the  absence  of 
analogy  for  such  a  peculiar  change,  by  which  one  portion  of  the 
same  organ  is  calcified,  and  the  rest  cornified  ;  and  again,  what  be¬ 
comes  of  these  cells  in  those  teeth  in  which  cementum  is  deposited 
in  bulk  over  the  surface  of  the  enamel  ?  According  to  the  statement 
of  Dr.  Magitot,  the  layer  of  cells  in  question  (external  epithelium 
of  the  enamel  organ)  is  atrophied  before  the  time  of  the  completion 
of  the  enamel  ;  a  fact  which,  if  confirmed,  is  fatal  to  Waldeyer’s 
explanation.  And  Dr.  Magitot,  in  his  most  recent  paper  on  the 
subject  (Journal  de  l’Anatomie,  Sec.,  1881),  gives  his  adherence  to 
the  view  that  it  is  cementum. 

Kolliker,  who  dissents  strongly  from  the  views  of  Waldeyer,  and 
admits  some  uncertainty  as  to  its  nature,  provisionally  regards  it  as 
a  continuous  and  structureless  layer  furnished  by  the  enamel  cells 
after  their  work  of  forming  the  fibrous  enamel  was  complete  ;  a 
sort  of  varnish  over  the  surface,  as  it  were. 

This  would  not  account  for  the  occurrence  of  lacunas  in  it. 


The  Gum. 

The  gum  is  continuous  with  the  mucous  membrane  of 
the  inside  of  the  lips,  of  the  floor  of  the  mouth,  and  of  the 
palate,  and  differs  from  it  principally  by  its  greater  density. 
Its  hardness  is  in  part  due  to  the  abundant  tendinous  fasci¬ 
culi  which  it  itself  contains,  in  part  to  its  being  closely 
bound  down  to  the  bone  by  the  blending  of  the  dense  fibrous 
fasciculi  of  the  periosteum  with  its  own.  The  fasciculi 
springing  from  the  periosteum  spread  out  in  fan-like  shape 
as  they  approach  the  epithelial  surface.  There  is  thus  no 


THE  DENTAL  TISSUES. 


115 


very  sharp  line  of  demarcation  between  the  gum  and  the 
periosteum  when  these  are  seen  in  section  in  situ. 

The  gum  is  beset  with  rather  large,  broad-based  papillae, 
which  are  sometimes  single,  sometimes  compound ;  the 
epithelium  is  composed  of  laminae  of  tesselated  cells,  much 
flattened  near  to  the  surface  ;  but  cylindrical  cells  form  the 
deepest  layer  of  the  epithelium,  the  rete  Malpighi. 

Small  round  aggregations  of  pavement  epithelium  are 
met  with  at  a  little  depth,  or  even  bedded  in  the  surface  * 
these,  the  “  glands  ”  of  Serres,  have  no  known  significance. 
In  the  neighbourhood  of  developing  tooth-sacs  epithelial 
aggregations  of  similar  appearance  are  to  be  met  with,  and 
in  such  spots  are  remains  of  the  neck  of  the  enamel  organ 
(cf.  page  145),  w7hich  has  undergone  this  curious  change 
subsequently  to  the  completion  of  its  original  function. 
The  gums  are  rich  in  vessels,  but  remarkably  scantily  sup¬ 
plied  with  nerves. 

At  the  necks  of  the  teeth  the  gum  becomes  continuous 
with  the  periosteum  of  the  internal  surface  of  the  alveoli 
into  which  it  passes  without  any  line  of  demarcation. 


The  Alveolo-Dental  Membrane. 

The  Alveolo-dental  Periosteum,  or  Root  membrane,  is  a 
connective  tissue  of  moderate  density,  devoid  of  elastic 
fibres,  and  richly  supplied  with  nerves  and  vessels. 

It  is  thicker  near  to  the  neck  of  the  tooth,  where  it 
passes  by  imperceptible  gradations  into  the  gum  and  peri¬ 
osteum  of  the  alveolar  process,  and  near  to  the  apex  of  the 
root.  The  general  direction  of  the  fibres  is  transverse  ;  that 
is  to  say,  they  run  across  from  the  alveolus  to  the  cemen- 
tum,  without  break  of  continuity,  as  do  also  many  capillary 
vessels ;  a  mere  inspection  of  the  connective  tissue  bundles, 
as  seen  in  a  transverse  section  of  a  decalcified  tooth  in  its 


116 


A  MANUAL  OF  DENTAL  ANATOMY. 


socket,  will  suffice  to  demonstrate  that  there  is  but  a  single 
“  membrane,”  and  that  no  such  thing  as  a  membrane  proper 
to  the  root  and  another  proper  to  the  alveolus  can  be  dis¬ 
tinguished  ;  and  the  study  of  its  development  alike  proves 
that  the  soft  tissue  investing  the  root,  and  that  lining  the 
socket,  are  one  and  the  same  thing  :  that  there  is  but  one 
“membrane,”  namely,  the  alveolo-dental  periosteum. 

At  that  part  which  is  nearest  to  the  bone  the  fibres  are 
grouped  together  into  conspicuous  bundles  ;  it  is,  in  fact, 
much  like  any  ordinary  fibrous  membrane.  On  its  inner 
aspect,  where  it  becomes  continuous  with  the  cementum,  it 
consists  of  a  fine  netwrork  of  interlacing  bands,  many  of 
which  lose  themselves  in  the  surface  of  the  cementum. 

But  although  there  is  a  marked  difference  in  histological 
character  between  the  extreme  parts  of  the  membrane,  yet 
the  markedly  fibrous  elements  of  the  outer  blend  and  pass 
insensibly  into  the  bands  of  the  fine  network  of  the  inner 
part,  and  there  is  no  break  of  continuity  whatever. 

The  actual  attachment,  both  to  the  cementum  and  to  the 
bone,  takes  place  by  means  of  the  connective  tissue  fibres, 
which  pass  right  into  the  hard  structures,  which  they 
traverse  for  some  distance,  and  in  this  situation  are  known 
as  Sharpey’s  fibres. 

They  pass  through  all  the  lamellae  of  the  cementum,  and 
there  are  appearances  of  shrinkage  in  dry  preparations 
which  would  lead  to  the  inference  that  they  were  not  very 
fully  calcified  ;  in  some  portions  of  the  cementum  it  seems 
to  be  almost  composed  of  them,  as  at  the  neck  of  a  tooth 
(Black).  This  writer  states  that  they  may  be  especially 
clearly  seen  in  the  pig,  and  that  “  they  are  the  principal 
fibres  of  the  peridental  membrane  included  in  the  cementum 
in  its  growth,  and  furnish  the  means  of  making  firm  hold  of 
the  peridental  membrane  upon  the  root  of  the  tooth.  They 
are  white  connective  tissue  fibres,  the  ends  of  which  are 
included  in  the  matrix  of  the  cementum  sufficiently  to  make 


THE  DENTAL  TISSUES.  '  117 


them  apparent  when  the  lime  salts  are  removed,  but  when 
both  are  calcified,  they  cannot  be  demonstrated  except  in 
cases  where  there  is  imperfect  calcification  of  the  fibres,  as 
has  been  mentioned  above.” 

The  thickness  of  the  membrane  appears  to  undergo  a 
diminution  with  age,  by  calcification  encroaching  upon  it 
from  both  the  side  of  the  bone  and  of  the  cementum. 

Malassez  (“Archiv  de  Physiologie,”  1885)  urges  that  an 
ordinary  periosteum  in  this  situation  would  be  too  tender  for 
the  purposes  of  mastication,  and  that  as  it  is  not  a  mere 
enveloping  membrane,  but  is  composed  of  fibrous  bundles, 
which  serve  to  sling  the  tooth  in  its  place,  it  should  be 
called  the  alveolodental  ligament ;  he  further  compares  it 
with  the  fibrous  bands  which  in  some  fishes  serve  to  tie  the 
tooth  down  to  the  bone  where  no  tooth  sockets  exist,  and 
holds  that  it  is  strictly  homologous  with  these.  Ranvier 
also  points  out  that  there  is  no  isolable  membrane  such  as 
there  is  on  a  long  bone,  and  compares  the  alveolar  cavity  and 
its  contents  to  a  very  large  medullary  space. 

At  the  surface  of  the  cementum  it  is  more  richly  cellular, 
and  here  occur  abundantly  large  soft  nucleated  plasm 
masses,  which  are  the  osteoblasts  concerned  in  making 
cementum,  and  which  by  their  offshoots  communicate  with 
plasm  masses  imprisoned  within  the  cementum. 

I  have  rarely  seen  the  fibres,  whether  in  longitudinal  or 
in  transverse  sections,  pass  straight  in  the  shortest  possible 
line  from  the  bone  to  the  cementum,  but  they  invariably 
pursue  an  oblique  course,  which  probably  serves  to  allow  for 
slight  mobility  of  the  tooth  without  the  fibres  being  stretched 
or  torn. 

The  blood  vessels  are  most  abundant  in  membrane  mid¬ 
way  between  the  bone  and  the  cementum,  or  rather  nearer 
to  the  latter ;  but  close  to  it  there  is  a  rich  capillary  plexus 
without  large  vessels.  A  good  many  of  the  arteries  enter 
the  apical  region,  and  break  up  to  go,  partly  to  the  tooth  pulp 


118 


A  MANUAL  OF  DENTAL  ANATOMY. 


The  vascular  supply  of  the  root  membrane  is,  according 
to  Wedl,  derived  from  three  sources ;  the  gums,  the  vessels 
of  the  bone,  and  the  vessels  destined  for  the  pulp  of  the 
tooth,  the  last  being  the  most  important. 

(b  Portion  of  the  side  of  the  root  of  a  tooth,  the  gum  and  alveolo- 
dental  membrane,  and  the  edge  of  the  bone  of  the  alveolus. 

A  band  of  fibres  is  seen  passing  over  the  surface  of  the  alveolus  and 
dividing,  some  to  pass  upwards  into  the  gum,  others  to  pass  more  directly 
across  to  the  cementum.  Numerous  orifices  of  vessels  cut  across  trans¬ 
versely  are  seen  between  the  tooth  and  the  bone. 


and  partly  to  the  periosteum,  some  of  them  reaching  right 
from  the  apex  to  the  gum  ;  they  anastomose  freely  with 
vessels  in  the  bone  and  with  those  of  the  gum,  so  that  the 
blood  supply  is  not  easily  interfered  with. 

Fig.  57  (l). 


THE  DENTAL  TISSUES. 


119 


The  nerve  supply  also  is  largely  derived  from  the  dental 
nerves  running  to  the  dental  pulps ;  other  filaments  come 
from  the  inter-alveolar  canals  (canals  in  the  bone,  contain¬ 
ing  nerves  and  vessels,  which  are  situated  in  the  septa 
separating  the  alveoli  of  contiguous  teeth). 

It  should  be  borne  in  mind  that  the  tooth  pulp  and  the 
tissue  which  becomes  the  root  membrane  have  sprung  from 
the  same  source,  and  were  once  .continuous  over  the  whole 
base  of  the  pulp.  A  recognition  of  this  fact  makes  it  easier 
to  realise  how  it  comes  about  that  their  vascular  and  nervous 
supplies  are  so  nearly  identical. 

Several  observers  have  laid  stress  upon  the  occurrence  of 
cells  upon  the  surface  of  the  cementum,  deep  down  in  the 
tooth  sockets,  which  are  unlike  osteoblasts,  but  are  very 
much  like  epithelial  cells.  It  is  claimed  by  von  Brunn 
that  the  enamel  organ  goes  far  below  the  region  where 
enamel  is  to  be  formed,  and  that  it  is  in  fact  co¬ 
extensive  with  the  dentine,  thus  necessarily  intervening 
between  the  dentine  and  the  Qement-forming  tissue ;  he 
describes  the  connective  tissue  bundles  as  growing  through 
it  to  attach  themselves  to  the  dentine,  and  thus  cutting  up 
the  remains  of  this  enamel  organ  into  small  isolated  areas, 
which  are  to  be  found  here  and  there  in  the  adult  alveolo- 
dental  periosteum. 

Dr.  Black  describes  another  type  of  cells  which  he  be¬ 
lieves  to  be  lymph  cells  lining  lymph  canals  ;  these  are 
always  found  close  to  cementum.  He  believes  also,  as 
corroborative  of  this  view,  that  he  has  been  able  to  trace 
pus  infiltration  along  these  chains  of  cells. 

The  human  tooth  is,  accepting  as  correct  the  researches 
of  Bodecker,  which  appear  in  every  way  deserving  of  credence, 
connected  with  the  living  organism  very  intimately,  even 
though  its  special  tissues  are  extra-vascular. 

For  blood  vessels  and  nerves  enter  the  tooth  pulp  in 
abundance  ;  the  dentine  is  organically  connected  with  the 


120 


A  MANUAL  OF  DENTAL  ANATOMY. 


pulp  by  the  dentinal  fibrils ;  these  are  connected  with  the 
soft  cement  corpuscles,  which  again  are  brought  by  their 
processes  into  intimate  relation  with  similar  bodies  in  the 
highly  vascular  periosteum. 

So  that  between  pulp  inside,  and  periosteum  outside,  there 
is  a  continuous  chain  of  living  plasm. 

Kolliker.  Gewebelehre. 

Manual  of  Histology,  annotated  by  Messrs.  Busk  and 
Huxley,  1853. 

Waldeyer.  Strieker’s  Histology.  1870. 

Frey.  Manual  of  Histology.  1874. 

Owen.  Odontography. 

Czermak.  Zeitschrift  f.  Wiss.  Zoologie.  1850. 

Neumann.  Zur  Kentniss  der  Normalen  Zahngeweber.  1853. 

Boll.  Untersuchungen  iiber  die  Zahnpulpa.  Archiv.  f.  Mikros. 
Anatom.  1868. 

Klein.  Atlas  of  Histology.  1880. 

Salter.  Dental  Pathology.  1874. 

Tomes,  J.  Lectures  on  Dental  Physiology  and  Surgery.  1848. 

On  the  Dental  Tissues  of  Rodentia  and  Marsupialia. 
Philos.  Transac.  1849,  1850. 

On  the  Presence  of  Soft  Fibrils  in  Dentine.  Philos. 
Transac.  1853. 

Tomes,  Charles  S.  On  Vascular  Dentine.  Phil.  Trans.  1878. 

On  the  Implantation  of  Teeth.  Proc.  Odontol. 
Soc.  1874—1876. 

On  Nasmyth’s  Membrane.  Quart.  Jour.  Micros. 
Science,  1872. 

Magitot  et  Legros.  Journal  de  l’Anatomie  de  M.  Ch.  Robin. 

1881. 

Retzius.  Mikrosk.  Undersok.  &c.  Stockholm,  1837,  and  Transla¬ 
tion  in  Nasmyth  on  the  Teeth,  1839. 

Nasmyth.  On  the  Teeth,  1839. 

Hertwig.  TTeber  der  Ban  der  Placoidschuppen  Jenaische  Zeit¬ 
schrift,  B.  viii. 

Von  Boas.  Zahne  der  Scaroiden,  Zeits.  f.  Wiss.  Zoologie,  B.  xxxii. 
Bodecker.  Dental  Cosmos.  1878. 

Lankester,  Ray.  On  the  Teeth  of  Micropteron.  Quart.  Journal 

Micros.  Science,  1857. 

Sudduth,  Xavier.  American  System  of  Dental  Surgery. 

Black.  Periosteum  and  Peridental  Membrane.  Chicago,  1887. 


CHAPTER  IV. 

THE  DEVELOPMENT  OF  THE  TEETH. 

The  development  of  the  teeth  is  a  process  which,  while 
subject  to  modifications  in  the  different  groups  of  verte¬ 
brates,  retains  nevertheless  in  all  certain  essential  charac¬ 
ters,  so  that  it  becomes  possible  to  embody  its  main  features 
in  a  general  account. 

Prior  to  the  commencement  of  any  calcification  there  is 
always  a  special  disposition  of  the  soft  tissues  at  the  spot 
where  a  tooth  is  destined  to  be  formed  ;  and  the  name  of 
“  tooth  germ  ”  is  given  to  those  portions  of  the  soft  tissue 
which  are  thus  specially  arranged.  All,  or  a  part  only,  of 
the  soft  structures  making  up  a  tooth  germ,  become  con¬ 
verted  into  the  dental  tissues  by  a  deposition  of  salts  of  lime 
within  their  own  substance,  so  that  an  actual  conversion  of 
at  least  some  portions  of  the  tooth  germ  into  tooth  takes 
place.  The  tooth  is  not  secreted  or  excreted  by  the  tooth 
germ,  but  an  actual  metamorphosis  of  the  latter  takes 
place.  The  details  of  this  conversion  can  be  better  dis¬ 
cussed  at  a  later  page  ;  for  the  present  it  will  suffice  to  say 
that  the  three  principal  tissues,  namely,  dentine,  enamel, 
and  cementum  are  formed  from  distinct  parts  of  the  tooth 
germ,  and  that  we  are  hence  accustomed  to  speak  of  the 
enamel  germ  and  the  dentine  germ  ;  the  existence  of  a 
special  cement  germ  is  asserted  by  Magitot,  but  as  yet  his 
descriptions  await  confirmation. 

In  many  anatomical  works  the  process  of  tooth  develop¬ 
ment  used  and  may  sometimes  still  be  found  to  be  divided 


122 


A  MANUAL  OF  DENTAL  ANATOMY. 


into  periods,  under  the  names  of  “papillary,”  “follicular,” 
and  “  eruptive  ”  stages. 

These  stages  are  based  upon  a  false  conception,  upon 
theories  now  known  to  be  incorrect,  and  may  advantageously 
be  absolutely  abandoned.  The  account  of  the  development 
of  the  teeth  given  in  the  following  pages  (based  in  the 
case  of  man  and  mammals  upon  the  researches  of  Kolliker, 
Thiersch,  and  Waldeyer;  in  the  case  of  reptiles  and  fishes, 
upon  those  of  Huxley  and  Santi  Sirena,  and  upon  Hertwig’s 
and  my  own),  will  be  found  to  differ  from  the  older  accounts 
published  by  a  deservedly  great  authority,  Professor  Owen. 
Modern  methods  of  research  have  disclosed  facts  heretofore 
not  demonstrable ;  yet  twenty  years  ago  Professor  Huxley 
demonstrated  in  a  remarkable  paper  the  incorrectness  of 
certain  of  the  theories  then  promulgated.  Of  the  general 
accuracy  of  the  following  description  I  am  however  fully 
satisfied,  and  most  of  the  facts  may  be  easily  verified  by  any 
one  desirous  of  so  doing. 

True  tooth  germs  are  not  formed  quite  upon  the  surface  (*)> 
but  are  always  situated  at  a  little  distance  beneath  it,  in 
some  creatures  ultimately  coming  to  lie  at  a  considerable 
depth.  Every  known  tooth  germ  consists  in  the  first  in¬ 
stance  of  two  portions,  and  two  only,  the  enamel  germ  and 
the  dentine  germ ;  and  these  are  derived  from  distinct 
sources,  the  former  being  a  special  development  from  the 
epithelium  of  the  mouth,  the  latter  from  the  more  deeply 
lying  parts  of  the  mucous  membrane.  Other  things,  such 
as  a  tooth  capsule,  may  be  subsequently  and  secondarily 
formed,  but  in  the  first  instance,  every  tooth  germ  consists 
of  an  enamel  germ  and  a  dentine  germ  only,  and  the 
simplest  tooth  germs  never  develop  any  additional  parts. 
The  existence  of  an  enamel  organ  in  an  early  stage  is  there¬ 
fore  perfectly  independent  of  any  subsequent  formation  of 

(fi  The  placoid  scales  of  embryonic  sharks  are,  however,  formed  on  the 
surface,  and  the  “germs”  covered  in  by  epithelium  only  (Hertwig). 


THE  DEVELOPMENT  OF  THE  TEETH. 


323 


enamel  by  its  own  conversion  into  a  calcified  tissue,  for  I 
have  shown  that  it  is  to  be  found  in  the  germs  of  teeth 
which  have  no  enamel ;  in  fact,  in  all  known  tooth  germs 
whatever. 

That  part  of  the  tooth  germ  destined  to  become  dentine 
is  often  called  the  dentine  papilla,  having  acquired  this 
name  from  its  papilliform  shape  ;  and  in  a  certain  sense  it 
is  true  that  the  enamel  organ  is  the  epithelium  of  the  den¬ 
tine  papilla.  Yet,  although  not  absolutely  untrue,  such  an 
expression  might  mislead  by  implying  that  the  enamel 
organ  is  a  secondary  development,  whereas  its  appearance 
is  contemporaneous  with,  if  not  antecedent  to,  that  of  the 
dentine  germ.  The  most  general  account  that  I  am  able 
to  give  of  the  process  is,  that  the  deeper  layer  of  the  oral 
epithelium  sends  down  into  the  subjacent  tissue  a  process, 
the  shape  and  structure  of  which  is,  in  most  animals,  dis¬ 
tinguishable  and  characteristic  before  the  dentine  germ  has 
taken  any  definite  form.  This  process  enlarges  at  its  end, 
and,  as  seen  in  section,  becomes  divaricated,  so  that  it  bears 
some  resemblance  to  an  inverted  letter  Y  ;  or  it  might  more 
truthfully  be  compared  to  a  bell  jar  with  a  handle ;  this 
constitutes  the  early  stage  of  an  enamel  germ  (see  Fig.  65), 
while  beneath  it  in  the  mucous  tissue,  the  dentine  germ 
assumes  its  papilliform  shape.  The  details  of  the  process 
varying  in  different  creatures,  I  will  at  once  proceed  to  the 
description  of  the  development  of  teeth  in  the  various 
groups. 

In  Elasmobranch  Fishes. — If  a  transverse  section 
through  the  jaw  of  a  dog-fish  (Scy Ilium  canicula)  be  ex¬ 
amined,  we  shall  find  that  the  forming  teeth  lie  upon  the 
inside  of  the  semi-ossified  jaw-bones,  the  youngest  being  at 
the  bottom  (Fig.  58) ;  progressing  upwards,  each  tooth  is 
more  fully  calcified  till,  on  passing  over  the  border  of  the 
jaw,  we  come  to  those  teeth  whose  period  of  greatest  useful¬ 
ness  is  passed  and  which  are  about  to  be  cast  off  in  the 


124 


A  MANUAL  OF  DENTAL  ANATOMY. 


course  of  that  slow  rotation  of  the  whole  tooth-bearing 
mucous  membrane  over  the  border  of  the  jaw,  which  is 
constantly  going  on. 

In  the  section  figured  there  are  four  teeth  advanced  in 
calcification,  while  beneath  them  are  four  tooth  germs  in 
earlier  stages ;  of  the  former  two  only  are  fully  protruded 
through  the  epithelium,  the  third  being  in  part  covered  in  ; 
the  remaining  teeth  are  altogether  beneath  the  surface  of 
the  epithelium,  and  therefore  shut  off  from  the  cavity  of  the 
mouth,  if  the  soft  parts  be  all  in  situ. 

All  the  teeth  not  fully  calcified  are  covered  in  and  pro¬ 
tected  by  a  reflexion  upwards  of  the  mucous  membrane  (c  in 
the  figure),  which  serves  to  protect  them  during  their  calci¬ 
fication. 

But  although  this  may  be  termed  a  fold  reflected  upwards, 
it  is  not,  as  was  supposed  by  Professor  Owen,  a  free  flap, 
detached  from  the  opposite  surface  on  which  the  teeth  are 
developing  ;  there  is  no  deep  open  fissure  or  pouch  running 
round  inside  the  jaw,  as  would  in  that  case  exist,  and  the 
epithelium  does  not  pass  down  on  the  one  side  to  the  bottom 
of  such  fissure,  and  then  ascend  upon  the  other  as  a  distinct 
layer.  Although  the  fold  is  very  easily  torn  away  from  the 
tooth  germs  which  it  covers  in,  yet  in  the  natural  condition 
it  is  attached,  and  there  is  no  breach  of  surface ;  the  epithe¬ 
lium  passing  across  from  the  jaw  to  cover  it  is  well  seen  in 
the  figure,  in  which  the  epithelial  layer  is  represented  as 
broken  just  at  the  point  (between  the  third  and  fourth 
teeth)  where  it  leaves  the  jaw  to  cross  over  on  to  the  surface 
of  the  flap. 

The  conditions  met  with  in  the  Elasmob ranch  fishes  are 
peculiarly  favourable  for  the  determination  of  the  homolo¬ 
gies  of  the  several  jjarts  of  the  tooth  germ  and  of  the  formed 
tooth  (1).  At  the  base  of  the  jaw,  where  the  youngest 
tooth  germs  are  to  be  found,  the  tissue  whence  the  dentine 

P)  Compare  the  description  of  the  placoid  dermal  spine  (page  2). 


THE  DEVELOPMENT  OF  THE  TEETH. 


125 


papillae  arise  blends  insensibly  with  that  making  up  the 
substance  of  the  thecal  fold  on  the  one  hand,  and  on  the 

Fig.  58  (l). 


other,  with  that  clothing  the  convexity  of  the  jaw  and  giving 
attachment  to  the  teeth. 

No  sharp  line  of  demarcation  at  any  time  marks  off  the 
base  of  the  dentine  papilla  from  the  tissue  which  surrounds 
it,  and  from  which  it  springs  up,  as  would  be  the  case  in 
mammalian  or  reptilian  tooth  germs ;  all  that  can  be  said 
is,  that  the  dentine  germs  are  cellular,  the  cells  being  large 
and  rounded,  while  in  the  rest  of  the  mucous  membrane 
the  fibrillar  elements  preponderate,  so  that  it  passes  by 

p)  Transverse  section  of  lower  jaw  of  a  Dog-fish.  a.  Oral  epithelium. 
b.  Oral  epithelium  passing  on  to  flap.  c.  Protecting  flap  of  mucous  mem¬ 
brane  (thecal  fold).  d.  Youngest  dentine  pulp.  e.  Youngest  enamel 
organ.  /.  Tooth  about  to  be  shed.  g.  Calcified  crust  of  jaw. 


126 


A  MANUAL  OF  DENTAL  ANATOMY. 


imperceptible  gradations  into  the  densely  fibrous  gum,  found 
on  the  exposed  border  of  the  jaw. 

The  dentine  germs,  and  consequently  the  dentine,  are 
indisputably  derived  from  the  connective  tissue  of  the 
mucous  membrane  immediately  subjacent  to  the  epithe¬ 
lium,  nor  can  it  be  doubted  that  the  enamel  organs  are 
simply  the  modified  epithelium  of  that  same  mucous 
membrane. 

Of  course  there  is  nothing  new  in  this  conclusion,  which 
had  been  already  arrived  at  by  the  study  of  other  creatures, 
but  the  sharks  happen  to  demonstrate  it  with  more  clear¬ 
ness  than  those  other  animals  in  whom  the  original  nature 
of  the  process  is  more  or  less  masked  by  the  introduction  of 
further  complexities. 

Hence  it  is  worth  while  to  study  carefully  the  relations 
of  the  epithelium  constituting  the  enamel  organs  with  that 
of  the  surface  of  the  mouth.  As  has  been  already  mentioned, 
in  the  normal  condition  of  the  part  there  is  no  deep  fissure 
on  the  inner  side  of  the  jaw,  but  the  epithelium  passes 
across  (from  the  interspace  between  the  third  and  fourth 
teeth  in  the  figure)  on  to  the  protecting  fold  of  mucous 
membrane  (c  in  fig.).  But  although  the  epithelium  is  re¬ 
flected  across  on  to  the  thecal  fold,  it  is  also  continued 
downwards  along  the  inner  side  of  the  developing  teeth  and 
tooth  germs,  giving  to  each  a  complete  investment,  and 
filling  up  the  whole  interval  between  the  tooth  germ  and  the 
thecal  fold.  The  epithelium  in  this  situation  does  not,  then, 
consist  simply  of  one  layer  going  down  on  the  one  side  and 
covering  the  tooth  germs,  and  then  reflected  up  at  the 
bottom  to  coat  the  inner  side  of  the  thecal  fold,  but  it  is  so 
arranged  as  to  have  relation  only  to  the  tooth  germs  ;  it  is 
termed  “  enamel  organs  ”  because  over  the  tooth  germs  these 
epithelial  cells  assume  a  marked  columnar  character,  and 
are  very  different  in  appearance  from  the  epithelium  else¬ 
where. 


THE  DEVELOPMENT  OF  THE  TEETH.  127 


The  terminal  portion  of  this  epithelium,  or,  in  other 
words,  the  youngest  enamel  germ,  forms  a  bell-like  cap  over 
the  eminence  of  mucous  membrane  connective  tissue  which 
constitutes  the  earliest  dentine  germ,  and  in  section  is  of 
the  form  shown  in  the  figure.  The  surface  next  to  the 
dentine  papilla  consists  of  elongated  columnar  cells,  with 
nuclei  near  to  their  attached  extremities,  while  the  rest  of 
its  substance  is  made  up  of  much  smaller  cells,  some  of 
which  have  inosculating  processes,  so  that  they  constitute 
a  sort  of  finely  cellular  connective  tissue,  very  different  in 
appearance  from  anything  met  with  in  mammalian  enamel 
organs.  It  is  sufficiently  consistent  to  keep  up  the  con¬ 
tinuity  of  all  the  enamel  organs,  even  when  displaced  in 
cutting  sections,  so  that  the  whole  might  be  described  as 
forming  one  composite  enamel  organ.  The  columnar  cells 
already  alluded  to  invest  the  whole  surface  which  is 
directed  towards  the  forming  teeth,  but  they  atrophy  some¬ 
what  in  the  interspaces  of  the  tooth  germs. 

Before  proceeding  further  in  the  description  of  the  deve¬ 
lopment  of  the  tooth  germs,  it  will  be  well  to  refer  to  a 
somewhat  earlier  stage  in  the  growth  of  the  Dog-fish,  in 
which  the  relation  subsisting  between  the  teeth  and  the 
dermal  spines  is  still  well  seen. 

On  the  lower  jaw  of  the  young  dog-fish  there  is  no  lip  ; 
hence,  as  is  seen  in  the  figure,  the  spines  which  clothe  the 
skin  come  close  to  the  dentigerous  surface  of  the  jaw. 

Although  there  are  differences  in  form  and  size,  a  glance 
at  the  figure  will  demonstrate  the  homological  identity  of  the 
teeth  and  the  dermal  spines.  As  the  dog-fish  increases  in 
size,  this  continuity  of  the  teeth  with  the  dermal  spines  on 
the  outside  of  the  head  becomes  interrupted  by  an  extension 
of  the  skin  to  form  a  lip ;  this  happens  earlier  in  the  upper 
jaw  than  in  the  lower,  and  at  first  the  spines  are  continued 
over  the  edge  and  the  inside  of  the  newly  formed  lip — from 
these  situations,  however,  they  soon  disappear.  In  structure, 


128 


A  MANUAL  OF  DENTAL  ANATOMY . 


— 

the  teeth  and  the  dermal  spines  are,  in  many  species,  very 
closely  similar  ;  the  latter  are,  however,  much  less  often 
shed  and  reproduced,  so  that  it  is  less  easy  to  find  them  in 
all  stages  of  their  growth ;  I  believe,  however,'  that  they 
follow  a  course  essentially  similar  to  that  of  the  teeth. 

It  is  stated  by  Gegenbaur  that  in  Selachia  the  mucous 

Fig.  59  (*). 


membrane  of  the  mouth  is  clothed  with  spines  of  a  structure 
similar  to  that  of  the  teeth,  and  that  these  spines  are  often 
limited  to  particular  regions,  extending  back  as  far  as  the 
pharynx — these  same  regions  in  Ganoids  and  Osseous  fishes 
being  occupied  by  conspicuous  teeth ;  and  Hertwig  has 
shown  that  the  dermal  spines  are  developed  in  a  manner 
precisely  analogous  to  that. described  in  the  teeth,  save  that 
the  germs  are  even  less  specialised. 

In  Teleostei  or  Osseous  Fishes. — In  passing  from 
the  consideration  of  the  development  of  the  tooth  germs  of 
Elasmobranch  to  those  of  Osseous  fishes,  the  first  difference 
to  be  noted  is  this  :  whereas  in  the  former  each  tooth  germ 
was,  so  far  as  the  enamel  germ  is  concerned,  derived  from  that 

f1)  Section  of  lower  jaw  of  young  Dog-fish,  showing  the  continuity  of  the 
dermal  spines  of  the  skin  under  the  jaw,  with  the  teeth  which  lie  above 
and  over  its  end. 


THE  DEVELOPMENT  OF  THE  TEETH. 


129 


of  the  next  older  tooth,  in  the  latter  each  enamel  germ  often 
arises  independently  and,  as  it  were,  de  novo .  At  all  events, 
so  far  as  my  own  investigations  go,  no  connection  has  been 
traced  between  the  germs  of  teeth  of  different  ages ;  but 
Heincke  says  that  in  the  Pike  new  enamel  organs  may  be 
derived  from  older  ones. 

This  independent  origin  of  an  indefinite  number  of  teeth, 


Fig.  60  (!). 


having  no  relation  to  their  predecessors,  is  only  certainly 
known  to  occur  in  the  osseous  fish  :  of  the  development  of 
the  teeth  of  Ganoid  fish  nothing  is  known. 

The  oral  epithelium,  which  varies  much  in  its  thickness 
and  in  other  characters  in  different  fishes,  sends  down  a 
process  which  goes  to  form  an  enamel  organ,  whilst  a  dentine 
papilla  in  rising  up  to  meet  it,  comes  to  be  invested  by  it  as 
with  a  cap.  The  after-history  of  the  process  depends  much 
on  the  character  of  tooth  which  is  to  be  formed.  If  no 
enamel,  or  but  a  rudimentary  coat  of  enamel,  is  to  be  formed, 
the  cells  of  the  enamel  organ  remain  small  and  insignificant, 
as  in  the  mackerel.  If,  on  the  other  hand,  a  partial  invest¬ 
ment  of  enamel  is  found  upon  the  perfected  tooth,  such 
for  instance,  as  the  little  enamel  tips  upon  the  teeth  of  the 

(!)  Tooth-germ  of  an  eel.  d.  Neck  of  enamel  organ,  e.  Enamel  cells. 
a.  Cap  of  enamel,  b.  Cap  of  dentine,  c.  Rudimentary  enamel  cells 
opposite  to  that  part  of  the  dentine  germ  where  no  enamel  will  be  formed. 


130 


A  MANUAL  OF  DENTAL  ANATOMY. 


eel  (see  Fig.  93),  then  the  after-development  of  the  enamel 
organ  is  very  instructive. 

Opposite  to  the  apex  of  the  dentine  papilla,  where  the 
enamel  cap  is  to  be,  the  cells  of  the  enamel  organ  attain  to 
a  very  considerable  size,  measuring  about  of  an  inch  in 
length ;  below  this  the  investing  cap  of  enamel  organ  does 
not  cease,  but  it  is  continued  in  a  sort  of  rudimentary  con¬ 
dition.  Thus,  although  the  enamel  organ  invests  the  whole 
length  of  the  dentine  papilla,  its  cells  only  attain  to  any 
considerable  size  opposite  to  the  point  where  the  enamel  is 
to  be  formed.  The  knowledge  of  this  fact  often  enables  an 
observer  to  say,  from  an  inspection  of  the  tooth  germ, 
whether  it  is  probable  that  the  perfected  tooth  will  be  coated 
with  enamel  or  not.  In  any  case  an  enamel  organ  will  be 
there,  but  if  no  enamel  is  to  be  formed,  the  individual  cells 
do  not  attain  to  any  considerable  degree  of  differentiation 
from  the  epithelium  elsewhere  ;  in  other  words,  the  whole 
enamel  organ  will  partake  of  the  character  of  the  lower 
portion  of  that  represented  in  the  figure  of  the  tooth  germ 
of  the  eel. 

Although  of  course  there  are  many  differences  of  detail 
arising  from  the  very  various  situations  in  which  teeth  are 
developed  in  fish,  so  great  uniformity  pervades  all  which 
I  have  examined,  that  we  may  at  once  pass  on  to  the  con¬ 
sideration  of  the  development  of  the  teeth  of  reptiles,  merely 
adding  that  it  is  not  altogether  true  to  say  that  the  teeth  of 
fish  in  their  development  exemplify  transitory  stages  in  the 
development  of  mammalian  teeth. 

In  Reptiles,  so  far  as  the  appearances  presented  by 
the  individual  germs  go,  there  are  few  differences  worthy 
of  note  to  be  found  by  which  they  are  distinguishable 
from  those  of  either  fish  or  mammals.  The  enamel 
organ  is  derived  from  the  oral  epithelium,  and  the  den¬ 
tine  organ  from  the  submucous  tissue  in  a  very  similar 
manner ;  nevertheless,  there  are  points  in  the  relation  which 


THE  DEVELOPMENT  OF  THE  TEETH 


131 


the  successional  tooth  germs  bear  to  one  another,  and  to  the 
teeth  already  in  situ ,  which  are  of  some  little  interest.  The 
constant  succession  of  new  teeth  met  with  amongst  almost 
all  reptiles  renders  it  easy  to  obtain  sections  showing  the 
teeth  in  all  stages  of  growth  :  upon  the  inner  side  of  the  jaw 
there  will  be  found  a  region  occupied  by  these  forming  teeth 


Fig.  61  (*). 


and  by  nothing  else,  which  maybe  called  “area  of  tooth  deve¬ 
lopment  ;  ”  this  is  bounded  on  the  one  side  by  the  bone  and 
teeth  wThich  it  carries,  and  on  the  other  by  a  more  or 
less  sharply  defined  wall  of  fibrous  connective  tissue.  In 
the  newt  for  example  (Fig.  61),  to  the  left  of  the  tooth  in 
use  are  seen  four  tooth  sacs,  in  serial  order,  the  youngest 
being  nearest  to  the  median  line  of  the  mouth.  As  the  sacs 
increase  in  size  they  appear  to  undergo  a  sort  of  migration 

(!)  Section  of  upper  jaw  of  Triton  cristcitus  (newt).  To  the  inner  side 
of  the  tooth  attached  to  the  bone  are  three  younger  tooth  germs. 

K  2 


132 


A  MANUAL  OF  DENTAL  ANATOMY. 


towards  the  edge  of  the  jaw,  while  simultaneously  new  ones 
are  constantly  being  developed  beyond  them.  In  the  newt, 
the  ingrowth  of  the  epithelium  is  obviously  the  first  step 
apparent ;  this  ingrowth  of  a  process  of  epithelium  takes 
place  in  close  relation  with  the  “neck”  of  an  older  enamel 
organ  (i.e.,  the  contracted  band  of  epithelium  which  remains 
for  some  time  connecting  the  new  enamel  organ  with  the 
epithelium  whence  it  was  derived).  New  enamel  organs  are 
therefore  not  derived  directly  from  the  epithelium  of  the 
surface,  but  from  the  necks  of  the  enamel  organs  of  their 
predecessors. 

In  the  newt,  the  developing  teeth  spread  out  for  a  con¬ 
siderable  distance  towards  the  palate,  and  thus,  being  free 
from  crowding,  the  relations  of  the  enamel  organs  of  three 
or  four  successional  teeth  of  serial  ages  may  be  studied  in  a 
single  section ;  and  the  arrangement  so  disclosed  may  be 
advantageously  compared  with  that  seen  in  the  dog-fish  (see 
Fig.  58). 

The  tooth  sac  of  the  newt  is  a  good  example  of  the  sim¬ 
plest  form  of  tooth  sac,  consisting  solely  of  an  enamel  organ 
and  a  dentine  germ,  without  any  especial  investment.  The 
“sac”  is  wholly  cellular,  and  on  pressure  breaks  up,  leaving 
nothing  but  cells  behind  it.  The  cells  of  the  enamel  organ 
are  large,  and  resemble  those  of  the  eel ;  the  teeth  of  newts- 
have  a  partial  enamel  tip,  like  those  of  the  fish  referred  to, 
but  differing  from  them  in  being  bifurcated,  as  is  very 
early  indicated  by  the  configuration  of  the  enamel  organ. 

In  the  frog  there  is  a  peculiarity  in  the  manner  in  which 
the  two  jaws  meet,  the  edentulous  lower  jaw,  which  has  no 
lip,  passing  altogether  inside  the  upper  jaw  and  its  sup¬ 
ported  teeth,  and  so  confining  the  area  of  tooth  develop¬ 
ment  within  very  narrow  limits.  Consequently  I  have  been 
unable  to  satisfy  myself  whether  the  new  tooth  germs,  or 
rather  their  enamel  organs,  are  derived  from  those  of  their 
predecessors,  or  spring  up  de  novo  ;  analogy  would  indicate 


THE  DEVELOPMENT  OF  THE  TEETH. 


133 


the  former,  but  appearances  tend  towards  the  latter  sup¬ 
position. 

In  the  lizards  the  new  tooth  germs  are  formed  a  very  long 
way  beneath  the  Surface,  so  that  the  neck  of  the  enamel 
organ  becomes  enormously  elongated,  for  the  dentine  papilla 
is,  just  as  in  the  newt,  situated  at  first  quite  at  the  level  of 
the  floor  of  the  area  of  tooth  development.  The  teeth  of 
the  lizards  have  a  more  complete  investment  of  enamel, 
hence  the  enamel  cells  are  developed  upon  the  side  of  the 
dentine  germ  to  a  much  lower  point  than  in  the  newt.  The 
germs  also  acquire  an  adventitious  capsule,  mainly  derived 
from  the  condensation  of  the  connective  tissue  around 
them,  which  is  pushed  out  of  the  way  as  they  grow  larger. 
The  further  progress  of  the  tooth  germ  being  identical  with 
that  of  mammalia,  its  description  may  be  for  the  present 
deferred. 

In  ophidian  reptiles  (snakes)  several  peculiarities  are  met 
with  which  are  very  characteristic  of  the  order.  A  snake’s 
method  of  swallowing  its  food  would  seem  to  render  the 
renewal  of  its  teeth  frequently  necessary ;  although  I  do 
not  know  of  any  data  by  which  the  probable  durability  of 
an  individual  tooth  could  be  estimated,  the  large  number 
of  teeth  which  are  developing  in  reserve,  all  destined  to 
succeed  to  the  same  spot  upon  the  jaws,  would  indicate  that 
it  is  short. 

I  have  seen  as  many  as  seven  successional  teeth  in  a  single 
section,  and  their  arrangement,  particularly  in  the  lower 
jaw,  which  undergoes  great  displacement  while  food  is  being 
swallowed,  is  very  peculiar.  The  numerous  successional 
tooth  sacs,  instead  of  being  sj^read  out  side  by  side,  as  in 
the  newt,  are  placed  almost  vertically,  and  in  a  direction 
parallel  with  the  surface  of  the  jaw-bone;  they  are,  more¬ 
over,  contained  in  a  sort  of  general  investment  of  connective 
tissue ;  a  species  of  bag  to  keep  them  from  displacement 
during  the  expansion  of  the  mouth.  .  „  , 


134 


A  MANUAL  OF  DENTAL  ANATOMY. 


The  inward  growing  process  of  oral  epithelium  enters  this 
case  of  tooth  sacs  at  its  top  ;  and  may  be  caught  sight  of 
here  and  there  as  its  prolongations  wind  their  way  by  the 
sides  of  the  tooth  sacs  to  the  bottom  of  the  area.  Here  the 
familiar  process  of  the  formation  of  an  enamel  organ  and 


Fig.  62  (p. 


dentine  papilla  may  be  observed,  in  no  essential  point  differ¬ 
ing  from  that  which  is  to  be  seen  in  other  animals. 

That  the  derivation  of  each  enamel  organ  is  from  a  part  of 
that  of  its  predecessor  is  very  obvious  ;  the  dentine  organs 
are  formed  in  relation  with  the  enamel  germs,  but  apparently 
independently  ofone  another. 

(P  Transverse  section  of  the  lower  jaw  of  common  English  Snake,  e. 
Inward  dipping  process  of  epithelium.  /.  Oral  epithelium.  1,2,  3,  &c. 
Tooth  germs  of  various  ages.  8.  Tooth  in  place,  cut  somewhat  obliquely, 
so  that  its  tip  apparently  falls  short  of  its  surface,  and  does  not  project 
above  the  mucous  membrane. 


THE  DEVELOPMENT  OF  THE  TEETH. 


135 


As  the  tooth  sacs  attain  considerable  dimensions,  a  curious 
alteration  in  position  takes  place ;  instead  of  preserving  a 
vertical  position,  they  become  recumbent,  so  that  the  form¬ 
ing  tooth  lies  more  or  less  parallel  with  the  long  axis  of  the 


jaw.  The  utility  of  such  an  arrangement  is  obvious  :  W'ere 
the  tooth  to  remain  erect  after  it  has  attained  to  some  little 
length,  its  point  would  probably  be  forced  through  the 
mucous  membrane  when  the  mouth  was  put  upon  the  stretch ; 
but  while  it  lies  nearly  parallel  with  the  jaw  no  such 
accident  can  occur. 

The  tooth  does  not  resume  the  upright  position  until  it 
finally  moves  into  its  place  upon  the  summit  of  the  bone. 


(b  Developing  teeth  of  a  Snake.  /.  Oral  epithelium,  e.  Neck  of  the 
enamel  organs,  b.  Dentine  pulp.  c.  Enamel  cells,  d.  Dentine.  1 ,  2. 
Very  young  germs.  3,  4.  Older  germs. 


136 


A  MANUAL  OF  DENTAL  ANATOMY. 


As  has  already  been  mentioned,  there  is  a  well-developed 
enamel  organ  with  large  enamel  cells  :  from  these  a  thin 
layer  of  enamel  is  formed,  and  thus  the  thin  exterior  layer 
npon  the  teeth  of  snakes  is  true  enamel,  and  not,  as  has 
been  usually  supposed,  cementum. 

Many  points  in  the  development  of  the  teeth  of  reptiles  I 
have  passed  over  very*  briefl}7  for  the  want  of  space ;  a  more 
full  account  of  my  observations  will  be  found  in  the  Philo¬ 
sophical  Transactions  for  1875, 

In  Mammalia  the  earliest  changes  which  will  ultimately 


Fig.  64  (J). 


result  in  the  formation  of  a  tooth  are  traceable  at  a  very  early 
period ;  before  ossification  has  set  in,  the  lower  jaw  consist¬ 
ing  solely  of  Meckel’s  cartilage  imbedded  in  embryonic  tissue, 
and  the  lateral  processes  which  become  the  upper  maxillary 
bones  having  but  just  reached  as  far  as  the  median  process 
which  constitutes  the  intermaxillary  bone.  That  is  to  say, 
about  the  fortieth  or  forty-fifth  day  (in  the  human  subject), 
in  the  situation  corresponding  to  the  future  alveolar  border, 
there  appears  a  slight  rounded  depression,  extending  the 
whole  length  of  the  jaw,  it  and  its  elevated  borders  being 

(b  Embyro  at  end  of  fifth  week,  after  Carpenter.  1,  2.  First  two 
visceral  arches,  a.  Superior  maxillary  process,  t.  Tongue,  b.  Eye. 
c.  Lateral  nasofrontal  process,  rtf.  Nasofrontal  process* 


THE  DEVELOPMENT  OF  THE  TEETH 


137 


formed  by  an  increase  in  the  thickness  of  the  layer  of  epi¬ 
thelial  cells;  while  in  transverse  sections  the  proliferation  of 
epithelial  cells  is  found  to  have  been  even  more  energetic  in 
a  direction  downwards  into  the  substance  of  the  jaw  than  it 
is  upwards,  so  that  a  cul-de-sac  of  epithelium  dips  into  the 
embryonic  sub-mucous  tissue.  (J) 

In  a  certain  sense,  then,  there  is  a  dental  groove,  but  it  is 
not  the  same  thing  as  that  described  as  such  in  the  text¬ 
books,  and  it  is  therefore  better  to  abstain  from  applying  that 
or  any  other  name  to  the  shallow  furrow  of  which  we  are 
now  speaking,  which  is  almost  filled  up  with  spherical  or 
flattened  cells,  the  deepest  layer  being,  however,  columnar 
cells.  From  the  bottom,  or  the  side  near  the  bottom  of  the 
depression,  an  inflection  of  epithelial  cells  takes  origin ; 
it  does  not  dip  downwards  vertically,  but  inclines  in¬ 
wards.  This  narrow  inflection  of  epithelium,  which  in 
section  closely  resembles  a  tubular  gland,  constitutes  the 
rudiment  of  the  future  enamel  organ  ;  a  proliferation  of  the 
cells  at  its  deepest  extremity  speedily  takes  place,  so  that  it 
expands,  attaining  somewhat  the  form  of  a  Florence  flask 
(Fig.  65).  It  should,  however,  be  noted,  that  while  the  in¬ 
flection  of  epithelium  takes  place  around  the  entire  circum¬ 
ference  of  the  jaw,  so  that  that  which  appears  in  sections 
like  a  tubular  gland  is  really  a  continuous  sheet  or  lamina  of 
epithelium,  the  dilatations  of  its  extremity,  which  I  have 
compared  to  a  Florence  flask,  occur  only  at  the  several  points 
where  teeth  will  ultimately  be  developed. 

The  cells  upon  the  periphery  are  columnar,  polygonal 
cells  occupying  the  central  area  of  the  enlargement.  Very 

(:)  The  epithelium  having  been  removed  by  maceration  or  by  keeping  a 
specimen  in  dilute  spirit,  a  groove  would  result,  and  this  is  probably  what 
was  seen  and  described  by  Groodsir  as  the  primitive  dental  groove”  : 
but,  as  the  student  will  gather  from  the  text,  there  is  at  no  time  any  such 
thing  as  a  deep  open  groove  like  that  described  by  him,  unless  it  results 
from  maceration  and  consequent  partial  destruction  of  the  specimen. 


138 


A  MANUAL  OF  DENTAL  ANATOMY: 


soon  the  terminal  enlargement,  as  it  grows  more  deeply 
into  the  jaw,  alters  in  form  ;  its  base  becomes  flattened, 

Fig.  65  {l). 

7  2 


and  the  borders  of  the  base  grow  down  more  rapidly  than 
the  centre,  so  that  its  deepest  portion  presents  a  concavity 

P)  Three  stages  in  the  development  of  a  mammalian  tooth  germ  (after 
Frey),  a.  Oral  epithelium  heaped  up  over  germ.  b.  Younger  epithelial 
cells,  c.  Deep  layer  of  cells,  or  rete  Malpighi,  d.  Inflection  of  epithelium 
for  enamel  germ.  e.  Stellate  reticulum,  f.  Dentine  germ.  g.  Inner 
portion  of  future  tooth  sac.  h.  Outer  portion  of  future  tooth  sac. 
i.  Vessels  cut  across.  Jc.  Bone  of  jaw. 


THE  DEVELOPMENT  OF  THE  TEETH. 


139 


looking  downwards;  it  might  be  compared  to  a  bell,  sus¬ 
pended  from  above  by  the  thin  cord  of  epithelium  which 
still  connects  it  with  the  epithelium  of  the  surface,  or  it 
might  in.  section  be  described  as  crescentic,  the  horns  of  the 
crescent  being  long,  and  looking  downwards.  Coincident 
with  the  assumption  of  this  form  by  the  enamel  germ,  is 
the  appearance  of  the  dentine  germ ;  but  it  will  facilitate 
the  description  of  the  process  to  pursue  a  little  farther 
the  development  of  the  enamel  organ. 

The  cells  on  its  periphery  remain  prismatic  or  columnar, 
but  those  in  its  centre  become  transformed  into  a  stellate 
network,  in  wdiich  conspicuous  nuclei  occupy  the  centre  of 
ramified  cells,  the  processes  from  which  anastomose  freely 
with  those  of  neighbouring  cells  (see  Fig.  66).  This  conver¬ 
sion  of  the  cells  into  a  stellate  reticulum  is  most  marked 
quite  in  the  centre  of  the  enamel  organ  ;  near  to  its  surfaces 
the  processes  of  the  cells  are  short  and  inconspicuous,  and  the 
whole  process  strikingly  recalls  the  phenomena  of  colloid 
degeneration  as  observed  in  certain  tumours. 

The  transformation  of  the  cells  occupying  the  centre  and 
constituting  the  bulk  of  the  enamel  organ  into  a  stellate 
reticulum  goes  on  progressing  from  the  centre  outwards,  but 
it  stops  short  of  reaching  the  layer  of  columnar  cells  which 
constitute  the  surface  of  the  enamel  organ,  next  to  the  den¬ 
tine  papilla  ;  a  narrow  layer  of  unaltered  cells  which  remain 
between  the  stellate  cells  and  the  columnar  enamel  cells 
constituting  the  “  stratum  intermedium.” 

Thus  far  all  the  cells  constituting  the  periphery  of  the 
enamel  organ  are  alike  :  they  are  columnar  or  prismatic, 
but  from  the  time  of  the  appearance  of  the  dentine  papilla 
those  which  come  into  relation  with  it  become  much  more 
elongated  and  greatly  enlarged,  while  those  round  the  outer 
or  convex  surface  of  the  enamel  organ  do  not  enlarge ; 
indeed,  according  to  some  authors,  they  even  commence  to 
atrophy  at  this  early  period.  The  cells  which  lie  like 


140 


A  MANUAL  OF  DENTAL  ANATOMY. 


a  cap  over  the  dentine  germ  or  “  papilla  ”  as  they  elongate 
and  their  nuclei  recede  to  their  extremities,  take  on  the 
character  to  be  presently  described  as  belonging  to  the 
“  enamel  cells,”  (enamel  epithelium,  internal  epithelium  of 
the  enamel  organ). 

The  enamel  organ,  then,  consists  (proceeding  from  with¬ 
out  inwards)  of  an  “  external  epithelium,”  a  “  stellate  reti¬ 
culum,”  a  “  stratum  intermedium,”  and  an  “  internal  epithe¬ 
lium,’  ’  the  external  and  internal  epithelia  being  continuous 
at  the  edges  or  base  of  the  enamel  organ,  while  at  its  summit 
the  external  epithelium  remains  still,  through  the  medium 
of  the  “  neck  of  the  enamel  organ,”  in  continuity  with  the 
cells  of  the  “stratum  Malpighi.” 

Thus  the  enamel  organ  is  entirely  derived  from  the  oral 
epithelium,  with  which,  by  means  of  its  “  neck,”  it  long 
retains  a  connection,  so  that  it,  and  whatever  products  it 
may  afterwards  give  rise  to,  are  obviously  to  be  regarded  as 
“epithelial  structures.”  But  it  is  the  enamel  organ  alone 
which  is  directly  derived  from  the  epithelium ;  the  origin  of 
the  dentine  germ  is  quite  distinct. 

In  the  embryonic  tissue  of  the  jaws,  some  little  distance 
beneath  the  surface,  and  at  a  point  corresponding  to  that 
ingrowth  of  cells  and  subsequent  enlargement  of  the  same 
which  goes  to  form  the  enamel  organ,  appears  the  first  trace 
of  a  dentine  germ.^)  This  appears  as  a  mere  increase  in 
the  opacity  of  the  part,  without  at  first  any  visible  structural 
change,  and  it  occupies  the  concavity  of  the  enamel  organ. 
Thus  the  dentine  germ  appears  early,  indeed  almost  simul¬ 
taneously  with  the  formation  of  a  definite  enamel  organ,  but 
the  enamel  organ  is  far  in  advance  of  it  in  point  of  structural 

f1)  The  term  “dental  papilla,”  although  eminently  convenient,  is  asso¬ 
ciated  with  an  erroneous  feature  of  the  older  views  upon  tooth  develop¬ 
ment  ;  where  it  is  employed  in  the  following  pages,  the  student  must 
guard  against  the  misconception  that  free  papillae  at  any  time  exist  in  any 
animal. 


THE  DEVELOPMENT  OF  THE  TEETH 


141 


differentiation,  and  the  earliest  changes  which  result  in  the 
formation  of  the  enamel  organ  are  strikingly  visible  before  a 
dentine  germ  can  he  discovered.  Hence  it  has  been  sug¬ 
gested  that  the  enamel  organ  governs  and  determines  the 
ultimate  form  of  the  tooth.  According  to  Dursy  the  dark 
halo  which  becomes  the  dentine  bulb  is,  like  the  inflection 
of  epithelium  which  forms  the  enamel  germ,  continuous  all 
round  the  jaw,  while  eventually  it  develops  into  prominences 
at  the  points  corresponding  to  the  enamel  germs  of  future 
teeth,  and  atrophies  in  their  interspaces. 

From  the  base  of  the  dentine  bulb  prolongations  pass  out¬ 
ward  and  slightly  upwards,  so  that  they  in  a  measure  embrace 
the  free  edge  of  the  enamel  organ,  and  at  a  somewhat  later 
period  they  grow  upwards  till  they  fairly  embrace  the  whole 
enamel  organ. 

These  prolongations  of  the  base  of  the  dentine  bulb  are 
the  rudiments  of  the  dental  sac.  In  their  origin,  therefore, 
the  dental  sac  and  the  dentine  organ  are  identical,  and 
spring  from  the  submucous  tissue  :  they  contrast  with  the 
enamel  organ,  which,  as  before  said,  is  derived  from  the  oral 
epithelium. 

To  recapitulate  briefly  the  facts  which  are  now  established 
beyond  all  question,  the  early  mammalian  tooth  germ  con¬ 
sists  of  three  parts,  one  of  which,  the  enamel  organ,  is 
derived  from  the  epithelium  of  the  surface  ;  the  other  two, 
the  dentine  organ  and  the  dental  sac,  originate  in  the  midst 
of  solid  embryonic  tissue  at  a  distance  from  the  surface,  the 
one  is  ecderonic  or  epiblastic,  and  the  other  enderonic. 

The  enamel  organ  is  formed  by  a  rapid  increase  of  cells  at 
the  bottom  of  a  process  which  dips  in  from  the  stratum 
Malpighi  of  the  oral  epithelium ;  the  dentine  germ  and  the 
dental  sac  are  formed  in  close  continuity  to  this  enamel 
organ  from  the  submucous  tissue. 

If  there  were  a  “  basement  membrane  ”  demonstrable  in 
the  mucous  tissues  at  this  early  period  (which  there  is 


142 


A  MANUAL  OF  DENTAL  ANATOMY. 


not)  the  enamel  organ  and  the  dentine  organ  would  lie  upon 
the  opposite  sides  of  it. 

The  description  of  the  appearance  of  the  several  parts  of 
the  tooth  germ  has  brought  us  to  the  period  at  which  cal¬ 
cification  first  commences,  but  before  proceeding  further, 
it  will  be  well  to  examine  more  minutely  the  structure  of 
the  several  organs  in  which  calcification  takes  place. 


ENAMEL  ORGAN. 

The  enamel  organ,  as  has  already  been  stated,  forms  a 
cap  -  like  investment  to  the  dentine  bulb,  and  it  is  itself 
thickest  over  the  apex  of  the  latter,  thinning  down  some¬ 
what  as  it  approaches  the  base. 

It  is  entirely  surrounded  by  an  epithelial  layer,  which 
upon  the  inner  surface  applied  to  the  dentine  bulb  consists 
of  much  elongated  columnar  cells,  and  takes  the  name  of 
internal  epithelium  of  the  enamel  organ ,  and  upon  its  outer 
surface  the  name  of  external  epithelium  of  the  enamel  organ. 
The  greater  bulk  of  the  enamel  organ  consists  of  a  stellate 
tissue,  which  passes  gradually  through  the  medium  of  a 
layer  of  rounded  cells,  the  stratum  intermedium ,  into  the 
enamel  cells ,  or  internal  epithelium.  The  essential  portion 
of  the  enamel  organ  is  this  layer  of  “  enamel  cells,”  which 
by  their  calcification  give  rise  to  the  enamel,  and  in  lower 
animals,  such  as  most  if  not  all  reptiles,  the  whole  enamel 
organ  is  represented  by  little  else  than  this  layer  of  “  enamel 
cells.” 

The  cells  of  the  internal  epithelium  (enamel  cells)  form 
an  exceedingly  regular  and  j)erfect  columnar  epithelium, 
the  individual  cells  becoming  by  result  of  their  mutual 
apposition  very  symmetrical  hexagons. 

They  are  four  or  five  times  as  long  as  they  are  broad,  and 


THE  DEVELOPMENT  OF  THE  TEETH. 


143 


the  nucleus,  which  is  large  and  oval,  occupies  that  end 
which  is  farthest  from  the  dentine.  It  is  said  by  Waldeyer 
that  the  sides  of  the  cells  only  are  invested  by  membrane, 
the  protoplasm  being  without  investment  at  its  two  ends. 

Towards  the  base  of  the  dentine  germ,  where  the  internal 
epithelium  merges  into  the  external  epithelium,  the  cells  are 
not  so  much  elongated,  and  they  then  pass  gradually  into 
the  cubical  form  of  these  latter  cells.  At  their  attached 
extremities  the  enamel  cells  are  prolonged  into  processes 


Fig.  66  l1). 


which  are  continuous  with  the  cells  of  the  stratum  inter¬ 
medium,  so  that  it  may  fairly  be  concluded  that  the  enamel 
cells,  as  they  are  used  up  in  the  formation  of  enamel,  are 
recruited  from  the  cells  of  this  layer. 

The  “  stratum  intermedium  ”  consists  of  cells  intermediate 
in  character  between  those  of  the  bordering  epithelium  and 
the  stellate  reticulum  ;  they  are  branched,  but  less  conspicu¬ 
ously  so  than  the  stellate  cells,  with  which  on  the  one  hand 
thev  are  continuous,  on  the  other  with  the  enamel  cells. 

The  stellate  cells  proper  are  characterised  by  the  great 
length  of  their  communicating  processes,  and  the  interspace 
of  the  meshes  is  occupied  by  a  fluid  rich  in  albumen,  so  that 
the  consistence  of  the  whole  is  little  more  than  that  of  jelly; 

P)  Cells  of  the  stellate  reticulum  of  the  enamel  organ.  From  Frey’s 
Histology. 


144 


A  MANUAL  OF  DENTAL  ANATOMY. 


as  the  structure  in  question  constitutes  the  major  part  in 
bulk  of  mammalian  enamel  organs,  these  have  been  called 
the  enamel  jellies,  or  enamel  pulps, 

The  function  and  destination  of  this  portion  of  the  enamel 
organ  is  not  very  clear  :  enamel  can  be  very  well  formed 
without  it,  as  is  seen  amongst  reptiles  and  fish,  and  even 
in  mammalia  it  disappears  prior  to  the  completion  of  the 
enamel,  so  that  the  external  and  internal  epithelia  come  into 
contact.  It  has  been  supposed  to  have  no  more  important 
function  than  to  fill  up  the  space  subsequently  taken  up  by 
the  growing  tooth.  (See  p.  166). 

The  external  epithelium  of  the  enamel  organ  is  composed 
of  cells  cubical  or  rounded  in  form,  and  is  of  little  interest 
save  in  that  it  is  a  matter  of  controversy  what  becomes  of 
it.  Waldeyer  holds  to  his  opinion  that,  after  the  disap¬ 
pearance  of  the  enamel  pulp  and  the  stratum  intermedium, 
it  becomes  applied  to  the  enamel  cells,  and  on  the  comple. 
tion  of  the  enamel  becomes  cornified  and  converted  into 
Nasmyth’s  membrane.  Kolliker  and  Legros  and  Magi  tot 
dissent  from  this  opinion,  the  latter  stating  that  the  atrophy 
of  these  cells  commences  early,  and  that  they  actually  dis¬ 
appear  prior  to  the  complete  atrophy  of  the  organ.  For 
reasons  which  I  have  given  elsewhere,  I  do  not  agree  with 
Waldeyer  in  this  matter,  but  rather  with  Magitot.  The 
external  epithelium  was  seen  by  Nasmyth,  Huxley,  and 
Guillot,  but  it  was  not  very  fully  described  until  investigated 
by  Robin  and  Magitot. 

So  simple  a  matter  as  the  vascularity  or  non-vascularity 
of  the  enamel  organ  is  not  yet  settled  ;  Wedl  asserts  that  it 
contains  no  vessels,  Magitot  and  Legros  sharing  this  opinion  ; 
Xavier  Sudduth  has  failed  uniformly  to  detect  vessels  in  it, 
but  Dr.  Lionel  Beale,  on  the  other  hand,  states  that  a 
vascular  network  lies  in  the  stratum  intermedium,  and  this 
is  confirmed  by  Professor  Howes  and  Mr.  Poulton  in  the  rat. 

The  inner  surface  of  the  enamel  organ,  where  it  is  applied 


THE  DEVELOPMENT  OF  THE  TEETH. 


145 


to  the  dentine  bulb,  presents  a  perfectly  smooth  outline,  but 
its  outer  surface  is  indented  by  numerous  papillary  projec¬ 
tions,  into  which  enter  blood  vessels  of  the  dental  sacculus. 
These  papillte  are  homologous  with,  and  continuous  with 
those  of  the  gum ;  they  may  sometimes  be  traced  along  the 
neck  of  the  enamel  germ,  and  it  is  believed  that  they 
exercise  an  important  influence  on  the  formation  of  the 


Fig.  67  0)- 


enamel,  to  which  I  shall  again  recur ;  but  their  existence  is 
denied  by  Dr.  Sudduth  during  the  active  period  of  the  organ. 

The  narrow  attenuated  line  of  cells  by  which  the  enamel 
organ  retains  its  connection  with  the  stratum  Malpighi, 
whence  it  was  derived,  varies  much  in  length  and  direction 
in  different  animals  ;  in  man  it  is  short  and  straight ;  in 
the  calf  it  is  larger,  and  undulates  in  its  course.  It  does 
not  remain  quite  that  simple  line  of  cells  of  which  it  con¬ 
sisted  when  first  formed,  but  varicosities,  made  up  of  poly 
hedral  cells,  bud  out  from  it. 

(!)  Dental  germ  of  temporary  tooth  of  an  Armadillo,  showing  its  enamel 
organ,  and  the  enamel  germ  of  the  successional  permanent  tooth  to  the 
left  of  it. 


L 


146 


A  MANUAL  OF  DENTAL  ANATOMY. 


Malassez  insists  much  upon  the  significance  of  rem¬ 
nants  of  epithelium  left  after  the  atrophy  of  the  enamel 
organ  ;  some  of  these  he  believes  that  he  has  found  in  the 
alveolo-dental  membrane.  This  is  confirmed,  as  to  develop- 

Fig.  68-  (J). 


ing  teeth,  by  Yon  Brunn,  Arcliiv  f.  Mik.  Anat.,  Bd.  xxix.,  who 
states  that  in  rodents  the  enamel  organ  extends  far  down, 
in  fact,  the  whole  length  of  the  roots,  and  figures  the  fibres 
of  the  alveolo-dental  periosteum  as  growing  through  it  to  take 
hold  of  the  cementum ;  but  it  seems  possible  that  these  cells 
are  the  same  which  are  by  Dr.  Xavier  Sudduth  held  to  be 
portions  of  a  lymphatic  system. 

The  origin  of  the  dental  germs  of  the  permanent  teeth 
remains  to  be  described  :  the  twenty  teeth  which  have 
deciduous  predecessors  being  derived  from  parts  of  the 

f1)  From  the  upper  jaw  of  a  kitten  about  the  time  of  birth,  a.  Oral 
epithelium.  b.  Bone  of  jaw.  c.  Neck-  of  enamel  organ.  d.  Dentine 
papilla,  e.  Enamel  cells.  /.  Stellate  reticulum,  h.  Tooth  germ  of  the 
permanent  tooth,  the  enamel  organ  of  which  is  derived  from  the  neck  of 
that  of  its  predecessor. 


THE  DEVELOPMENT  OF  THE  TEETH. 


147 


germs  of  these,  the  twelve  true  molars  having  a  distinct 
origin.  About  the  sixteenth  week  of  intra  uterine  life,  from 
the  neck  of  cells  which  connects  the  enamel  organ  of  the 
temporary  enamel  germ  wTitli  the  stratum  Malpighi,  there 
buds  out  a  secondary  inflection  of  epithelium,  similar  in 
appearance  to  the  first  rudiment  of  the  enamel  germ  of 
the  milk  tooth ;  it  passes  down  to  the  inner  side  of  the 
temporary  tooth  sac,  and  by  undergoing  a  series  of  changes 
in  all  respects  analogous  with  those  resulting  in  the  forma¬ 
tion  of  the  temporary  tooth  germ,  gives  rise  to  the  perma¬ 
nent  tooth  germ. 

The  preceding  figure  (Fig.  68)  represents  the  enamel  germ 
for  a  permanent  tooth  budding  off  from  the  neck  of  the 
enamel  organ  of  the  temporary  tooth.  Many  differences  of 
detail,  such  as  the  point  •  at  which  they  arise,  the  depth 
to  which  they  penetrate  into  the  surrounding  parts,  and 
■other  such  characteristics,  exist  not  only  between  the  germs 
of  teeth  of  different  animals,  but  even  between  those  of 
teeth  situated  in  different  parts  of  the  mouth  of  the  same 
animal,  so  that  but  little  importance  is  to  be  attached  to 
them. 

I  am  indebted  to  Mr.  J.  Andrew  for  a  photograph  of  this 
section  taken  from  the  upper  jaw  of  a  foetus  four  or  five 
months  old,  which  shows  the  origin  of  the  germs  of  the  six- 
year  molar  well. 

At  the  left-hand  side  of  the  figure  is  seen  the  germ  of 
the  first  temporary  molar,  next  that  of  the  second  temporary 
molar,  whilst  from  this  is  given  off  the  enamel  organ  of  the 
six-year  permanent  molar. 

Thus  the  second  temporary  molar  germ  gives  off  two  off¬ 
sets,  the  one  directed  to  its  inner  side,  which  goes  to  form 
the  germ  for  the  second  bicuspid,  and  one  directed  back¬ 
wards  for  the  six-year  old  molar.  From  this  again  will  be 
given  off  the  germ  for  the  second  molar,  and  from  that  the 
germ  for  the  wisdom  tooth. 

l  2 


148 


A  MANUAL  OF  DENTAL  ANATOMY. 


The  germ  of  the  second  permanent  molar  is  believed  to 
originate  about  the  third  month  after  birth,  whilst  the 


Fig.  -69  (J)- 


enamel  germ  of  the  wisdom  tooth  succeeds  after  a  much 
longer  interval,  i.e.,  about  the  third  year  (Magitot). 


Dentine  Organ. 

The  dentine  germ,  or  dentine  bulb,  of  which  the  origin 
has  been  already  described,  at  first  was  nothing  more  than 
a  part  of  the  myxomatous  tissue  of  the  jaw  which  had  become 
more  rich  in  vessels  and  cells  than  other  neighbouring  parts, 
but  did  not  present  any  structures  essentially  different  from 
those  found  around  it.  It  very  speedily  assumes  the  form 
of  the  apex  of  the  future  tooth,  becoming,  if  it  be  a  canine, 
simply  conical,  if  a  tooth  with  two  cusps,  bicuspid  ;  and 
coincidently  with  these  changes  the  layer  of  cells  forming 
its  surface,  which  is  in  close  relation  with  the  enamel  cells, 
becomes  differentiated  from  the  parts  beneath  it. 

These  cells,  which  become  dentine  by  their  calcification, 
form  a  very  distinct  layer,  which,  after  the  commencement 

d)  From  upper  jaw  of  human  foetus.  Longitudinal  section.  Mr.  Andrew’s 
specimen,  a.  Germ  of  first  temporary  molar,  b.  Germ  of  second  tem¬ 
porary  molar,  c.  Cord  and  germ  for  6-year  permanent  molar.  This  figure 
has  been  lettered  upside  down. 


THE  DEVELOPMENT  OF  THE  TEETH. 


149 


of  calcification,  adheres  more  strongly  to  the  formed  cap  of 
dentine  than  to  the  rest  of  the  pulp,  and  so  is  often  pulled 
away  with  the  former  when  the  two  are  separated ;  hence 
this  layer  of  cells  has  obtained  the  name  of  “  membrana 
oboris,”  or  membrane  of  the  ivory ;  but  the  student  must 
beware  of  falling  into  the  mistake  of  supposing  that  it  really 
is  a  “  membrane”  properly  so  called. 


Fig.  70  {}). 


Before  entering  upon  a  detailed  description  of  the  trans¬ 
formation  which  the  various  cells  undergo  in  their  con¬ 
version  into  enamel,  dentine,  or  cementum,  it  will  not  be 
out  of  place  to  say  a  few  words  relative  to  the  process  of 
calcification  generally. 

(!)  Tooth  sac  of  a  calf.  a.  Tooth  sac.  a1  a2.  Its  outer  and  middle 
portions,  b.  Stellate  cells  of  enamel  organ,  c.  External  epithelium  of 
enamel  organ,  cl.  Internal  epithelium  of  enamel  organ,  e.  Odontoblasts. 
f.  Dentine  bulb  in  papilla,  cj.  Vessels  in  dentine  bulb.  i.  Points  where 
the  sac  becomes  fused  with  the  base  of  the  dentine  papiila. 


150 


A  MANUAL  OF  DENTAL  ANATOMY. 


But  before  doing  so  it  may  perhaps  assist  the  student,  who  may 
be  perplexed  in  endeavouring  to  reconcile  the  statements  of  various 
authors,  to  give  a  succinct  history  of  the  views  from  time  to  time 
set  forth.  (*) 

Before  the  time  of  Goodsir  (1838),  the  development  of  the  teeth 
was  described  by  Raschkow  somewhat  vaguely  as  proceeding  under¬ 
neath  the  mucous  membrane  ;  he  did  not,  however,  trace  out  in 
what  precise  manner  the  several  parts  of  the  tooth  germ  originated. 
The  papers  of  Goodsir  giving,  in  the  place  of  somewhat  vague  and 
general  notions,  a  very  definite  and  intelligible  description  of  ob¬ 
servations,  was  accepted  without  question  by  most  anatomists,  if 
not  by  all.  Accordingly  we  find  in  all  the  text-books  at  and  after 
that  period,  and  in  some  even  at  the  present  day,  the  description 
given  by  Goodsir  reproduced  almost  without  alteration,  so  that  it 
will  be  worth  while  to  briefly  relate  what  his  views  were. 

He  believed  that  at  an  early  period  in  foetal  life  there  appeared 
a  continuous  open  groove,  running  round  the  whole  circumference 
of  the  jaws ;  that  from  the  bottom  of  this  groove  there  arose  iso¬ 
lated  and  uncovered  papillae,  corresponding  in  number  to  the  milk 
teeth  ;  that  these  papillae  became  covered  in  by  the  deepening  of 
the  groove  and  the  meeting  of  its  two  edges  over  their  tops,  whilst 
at  the  same  time  transverse  septa  were  formed,  so  that  the  several 
papillae  became  enclosed  in  their  own  separate  follicles.  With  the 
details  of  the  process  as  described  by  him  we  are  not  concerned  ;  it 
will  suffice  to  remember  that  he  distinguished  the  four  stages  : 
a  primitive  dental  groove,  a  papillary  stage,  a  follicular  stage, 
and  an  eruptive  stage  (the  latter  of  course  at  a  long  subsequent 
period). 

Hot  only  were  these  views  accepted  quite  without  question,  but 
they  were  even  extended  to  explain  the  development  of  the  teeth 
in'  Reptiles  and  Fishes,  and  thus  in  the  Odontographies  of  Professor 
Owen  and  Professor  Giebel  may  be  found  accounts  of  the  develop¬ 
ment  of  the  teeth  in  reptiles  and  fish  which  are  perfectly  in  accord 
with  Goodsir’s  theory,  but  which  in  fact  are  far  more  inaccurate 
than  the  same  theories  were  as  applied  to  mammalian  teeth. 

Even  so  careful  a  writer  as  Professor  Huxley,  who  was  the  first 
to  point  out  that  these  stages  really  did  not  exist  either  in  the  frog, 
the  mackerel,  or  certain  other  fish,  accepted  them  without  question 
as  true  of  mammalia.  Marcusen  (2)  (1849)  gave  upon  the  whole  a 

(*)  After  the  present  summary  had  been  partly  prepared,  the  author 
met  with  the  very  excellent  resume  given  by  Messrs.  Legros  and  Magitot, 
from  which  he  has  received  much  assistance. 

(2)  In  the  resume  given  by  Messrs.  Legros  and  Magitot,  before  referred 
to,  due  credit  is  not  given  to  the  papers  of  Marcusen  and  Huxley  (1849, 
1854)  (although  they  are  alluded  to),  and  it  appears  to  me  that  too  much 
is  given  to  that  of  Ratalis  Guillot  (1858). 


THE  DEVELOPMENT  OF  THE  TEETH. 


151 


correct  account  of  the  process,  referring  the  enamel  to  the  oral  epi¬ 
thelium,  and  Professor  Huxley  (1854),  whilst  demonstrating  that 
the  stage  of  free  papillge  was  not  to  be  found  in  certain  fish  and 
reptiles  (a  fact  also  made  out  in  the  newt  by  Dr.  Beale),  clearly  and 
strongly  expressed  the  same  view  as  to  the  origin  of  the  enamel 
organ,  and  hence  of  the  enamel.  And  whilst  regretting  that  their 
hold  upon  the  minds  of  anatomists  has  been  so  strong  as  to  en¬ 
courage  deductions  therefrom  going  wider  and  wider  of  the  mark,  I 
would  not  be  understood  to  set  small  value  upon  the  observations 
of  Arnold  and  Goodsir.  They  were  a  great  step  in  advance,  and 
were  as  accurate  as  the  methods  of  investigation  then  in  use  would 
allow  of  :  moreover,  the  error  in  observation  is  very  easy  to  account 
for,  as,  the  epithelium  having  peeled  off  as  a  result  of  decomposition, 
or  the  use  of  weak  spirit,  the  state  of  things  left  does  not  widely 
differ  from  that  described  by  Goodsir. 

The  subject  rested  for  many  years  without  further  advances,  but 
in  1868  Professor  Kolliker  demonstrated,  beyond  all  cavil,  the  real 
origin  of  the  enamel  organ  and  its  relations  to  the  oral  epithelium, 
the  dentine  organ,  and  the  dental  sac. 

His  views,  substantially  correct,  have  been  elaborated  by  Wal- 
deyer,  Kollmann,  Hertz,  Legros  and  Magitot,  Wedl,  and  others,  but 
only  in  minor  particulars  have  they  been  modified. 

The  development  of  the  teeth  of  reptiles  was  found  by  a  pupil  of 
M.  Kolliker’s,  M.  Santi  Sirena,  to  have  several  features  in  accord 
with  that  of  mammalian  teeth ;  my  own  researches  on  the  teeth  of 
Batrachia  and  Fish  and  Beptiles,  elsewhere  detailed,  have  proved  a 
striking  general  similarity  in  the  process  throughout  the  vertebrate 
kingdom . 

Dental  Follicle. — In  the  foregoing  account  little  men¬ 
tion  has  been  made  of  the  tooth  follicle  or  tissue  forming  a 
capsule-like  investment  around  the  dentine  germ  and  enamel 
organ.  At  an  early  period  of  development  the  tissue  form¬ 
ing  the  dentine  papilla  of  a  mammalian  tooth  is  seen  to  be 
prolonged  outwards  and  upwards  from  its  base  (see  h  in 
Fig.  65) ;  these  processes  appear  to  grow  rapidly  upwards, 
so  as  to  embrace  the  enamel  organ ;  but  whether  this  is 
really  so,  or  whether  it  is  merely  that  the  ill-defined  tissue 
in  which  the  dentine  forming  organ  has  itself  originated  is 
in  this  region  also  becoming  more  pronounced,  it  is  hard  to 
say  ;  probably  the  latter  is  the  more  true.  This  up-growth 
from  the  base  of  the  dentine  papilla  is  the  first  appearance 
of  a  special  dental  sacculus,  which  is  thus  derived  from 


152 


A  MANUAL  OF  DENTAL  ANATOMY. 


sources  identical  with  that  of  the  formative  organ  of  the 
dentine. 

While  these  changes  are  going  on,  the  tooth  sac  is  becoming 
lodged  in  a  widely  open  gutter  of  bone,  which  is  being  rapidly 
formed  at  its  sides  and  under  its  base.  If  at  this  stage 
(see  Fig.  71)  the  gum  be  stripped  off  the  jaws,  the 
developing  tooth  capsules  are  torn  off  with  it,  and 
are  inseparable  from  it  except  by  actual  cutting,  thus 
leaving  the  gutter  of  bone  quite  bare  and  empty.  In  fact 
the  capsule  or  sac  which  encloses  the  tooth  germ  consists  of 
almost  the  whole  of  the  connective  tissue  which  intervenes 
between  the  special  dentine  and  enamel  germs  and  the  bone, 
which  latter  is  originating  deep  in  the  tissues  and  indepen¬ 
dently  of  the  periosteum,  which  is  not  yet  differentiated. 

In  the  first  instance  the  follicle  wall  is  only  distinguished 

V 

from  the  connective  tissue  external  to  it  by  being  somewhat 
richer  in  cells,  vessels,  and  fibrillar  elements  ;  being,  in  fact, 
more  condensed  or  more  compact.  The  sacs,  when  at  their 
fullest  development,  are  divisible  into  two  layers,  an  outer 
thin  firm  wall,  and  an  inner  looser  tissue,  not  very  dense.  At 
the  base  of  the  tooth  sac,  the  follicle  wall  is  not  separable 
nor  distinguishable  from  the  base  of  the  dentine  papilla 
with  which  it  blends.  The  follicle  wall  is  richly  vascular ; 
and  over  the  surface  of  the  enamel  organ  it  is  prolonged 
inwards  in  the  form  of  villous  or  papilliform  eminences  (8 
in  Fig.  71),  projecting  into  the  external  epithelium  of  the 
enamel  organ  ;  to  these  prominences,  which  are  analogous  to 
the  papillse  on  the  free  surface  of  the  gum,  some  authors 
attach  much  importance,  as  having  an  influence  upon  the 
direction  of  the  enamel  prisms,  and  so  regulating  the 
pattern  formed  ;  but  this  view  is  by  no  means  universally 
accepted.  The  internal  or  softer  and  looser  portion  of  the 
follicle  wall,  which  has  a  consistency  but  little  firmer  than 
that  of  the  stellate  reticulum  of  the  enamel  organ,  is  much 
developed  in  Ruminants,  where  there  is  to  be  a  deposition 


Fig.  71  (*) 


(!)  Transverse  Section  of  the  Lower  Jaw  and  Developing  Back  Tooth  of  a  Lamb, 
copied  from  Waldeyer  (Henle’s  Zeitschrift  f.  Rat.  Med.  1865).  In  its  outlines  the  figure  is 
faithful  to  nature  ;  it  is  so  far  diagrammatic  that  more  of  structure  than  could  be  seen  with  the 
magnifying  power  employed  is  introduced. 

1,  Dentine  germ,  with  its  border  of  odontoblasts.  2.  Formed  dentine.  8.  Formed  enamel. 
4.  Points  where  the  inner  epithelium  and  the  outer  epithelium  of  the  enamel  become 
continuous.  5.  Enamel  cells  or  internal  epithelium.  6.  External  epithelium  of  enamel 
organ.  7.  Stellate  reticulum  of  enamel  organ.  8.  Papillary  projections  into  the  enamel 
organ.  9.  Connective  tissue  around  the  sac,  becoming  continuous  above  with  that  of  the 
gum  (9a) ;  this  constitutes  wliat  is  called  the  tooth  sac.  10.  Vessels  and  nerves  of  the 
jaw.  11.  Bone  of  lower  jaw.  12.  Periosteum  of  the  jaw.  13.  Heap  of  epithelium  over 
the  young  tooth.  14.  External  skin  with  its  epidermis.  15.  Muscular  bundles  from  floor 
of  mouth. 


[To  face  p.  152. 


THE  DEVELOPMENT  OF  THE  TEETH, 


153 


of  coronal  cement.  This  differentiation  of  a  portion  of  the 
dental  sac  is  thought  by  Messrs.  Legros,  Robin,  and  Magitot 
to  be  sufficiently  pronounced  to  justify  its  designation  as  a 
distinct  “  cement  organ.” 


The  Cement  Organ. 

Cementum  is,  according  to  these  authors,  developed,  just 
as  bone  is,  in  two  distinct  methods. 

Fig.  72  (l). 


• 

Where  it  is  not  to  be  very  thick,  and  is  to  clothe  roots, 
the  ossification  takes  place  in  membrane  (the  alveolo- 
dental  periosteum),  but  where  it  is  to  form  a  thick  layer 
over  the  crown,  as  in  Ruminants,  a  cartilaginous  cement 
organ  is  formed,  and  we  have  a  calcification  analogous  to 
formation  of  bone  in  cartilage. 

Thus  the  cement  organ  is  found  in  those  animals  only 

f1)  Cement  organ  of  a  calf  (after  Magitot).  a.  Fibroid  matrix. 
b.  Cartilage  cells  and  capsules. 


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156 


A  MANUAL  OF  DENTAL  ANATOMY. 


which  have  coronal  cement,  such  as  the  Herbivora.  In  a 
calf  embryo  about  the  time  that  dentine  calcification  is 
commenced,  there  may  be  distinguished  beneath  the  follicle 
wall  and  above  the  enamel  organ  a  greyish  layer  of  tissue, 
thick  enough  to  be  distinguishable  with  the  naked  eye,  and 
of  firmer  consistence  than  the  enamel  organ,  from  which  it 
also  differs  in  being  richly  vascular. 

But  though  it  exists  at  this  early  period,  it  is  not  till 
later,  when,  after  the  completion  of  the  dentine  and  enamel 
immediately  beneath  it,  its  own  function  is  about  to  come 
into  play,  that  it  attains  to  its  characteristic  structure. 
This  M.  Magi  tot  designates  as  fibro-cartilaginous,  as  there 
appear  in  it  characteristic  cartilage  cells  or  chondroplasts, 
containing  one,  two,  or  rarely  three  cells,  which  have 
spherical  or  ovoid  nuclei. 

In  those  creatures  which  have  cementum  upon  the  roots 
of  the  teeth  only,  no  special  cement  organ  exists,  but  osteo¬ 
blasts  which  calcify  into  cementum  are  furnished  by  the 
tooth  sac. 

It  is  said  that  the  inner  laver  of  the  tooth  sac  is  concerned 

*> 

in  the  formation  of  the  cement ;  that  the  outer  layer,  con¬ 
jointly  with  the  surrounding  connective  tissue,  is  converted 
into  the  alveolo-dental  periosteum,  but  I  cannot  myself 
recognise  the  justice  of  this  distinction  in  practice.  In 
human  teeth  the  parts  of  the  follicle  wall  or  sac  cease  to  be 
distinctly  distinguishable  at  a  comparatively  early  period, 
and  their  importance  is  not  such  as  to  call  for  very  detailed 
description. 

Another  structure,  once  thought  important,  and  now 
known  to  be  a  mere  bundle  of  dense  fibrous  tissue,  is  the 
“  gubernaculum .”  The  permanent  tooth  sacs,  during  their 
growth,  have  become  invested  by  a  bony  shell,  which  is 
complete,  save  at  a  point  near  their  apices,  where  there  is  a 
foramen.  Through  this  foramen  passes  a  thin  fibrous  cord, 
very  conspicuous  when  the  surrounding  bone  is  broken 


THE  DEVELOPMENT  OF  THE  TEETH. 


157 


away,  which  is  called  the  “ gubernaculum”  from  the  notions 
entertained  by  the  older  anatomists  that  it  was  concerned 
in  directing  or  effecting  the  eruption  of  the  tooth.  The 
gubernacula  of  the  front  permanent  tooth  sacs  perforate 
the  alveolus  and  blend  with  the  gum  behind  the  necks  of 
the  corresponding  milk  teeth  ;  those  of  the  bicuspids  unit¬ 
ing  with  the  periosteum  of  the  alveoli  of  their  deciduous 
predecessors. 


Calcification. 

A  tissue  is  said  to  be  “  calcified  ”  when  the  organic  struc¬ 
tures  of  which  it  is  composed  are  hardened  and  stiffened  by 
impregnation  with  salts  of  lime.  The  impregnation  with 
lime  salt  may  go  on  so  far  that  the  residual  organic  matrix 
is  reduced  to  a  very  small  proportion,  as  is  exemplified  in 
the  case  of  adult  enamel,  in  which  the  organic  constituents 
make  up  only  from  one  to  three  per  cent,  of  the  whole,  so 
that  practically  the  enamel  wholly  disappears  under  the 
influence  of  an  acid ;  or  the  organic  matrix  may  persist  in 
sufficient  quantity  to  retain  its  structural  characteristics 
after  the  removal  by  solution  in  an  acid  of  its  salts,  as  is 
the  case  with  dentine,  bone,  and  cementum.  There  are 
two  ways  in  which  a  calcified  structure  may  be  built  up  ; 
the  one  by  the  deposition  of  the  salts  in  the  very  substance 
of  a  formative  organ,  which  thus  become  actually  converted 
into  the  calcified  structure ;  the  other  by  a  formative  organ 
shedding  out  from  its  surface  both  the  organic  and  inorganic 
constituents,  and  thus,  so  to  speak,  excreting  the  resultant 
tissue. 

An  example  of  the  latter  method  is  to  be  found  in  the 
shells  of  many  mollusks,  in  which  the  mantle  secretes  the 
shell,  and  is  able  to  repair  fractures  in  it,  without  itself 
undergoing  any  apparent  alteration ;  while  the  formation  of 


158 


A  MANUAL  OF  DENTAL  ANATOMY. 


dentine,  bone,  and  enamel  (*)  are  examples  of  calcification 
by  conversion. 

The  insoluble  salts  of  lime  are  altered  in  their  behaviour 
by  association  with  organic  compounds,  a  fact  which  was 
first  pointed  out  by  Rainie,  and  has  been  more  recently 
worked  out  by  Professor  Harting  and  Dr.  Ord. 

If  a  solution  of  a  soluble  salt  of  lime  be  slowly  mixed 
with  another  solution  capable  of  precipitating  the  lime,  the 
resultant  lime  salt  will  go  down  as  an  amorphous  powder, 
or,  under  some  circumstances,  in  minute  crystals.  But  in 
the  presence  of  gelatine,  albumen,  and  many  other  organic 
compounds,  the  form  and  physical  character  of  the  lime 
salts  are  materially  altered,  and  in  the  place  of  an  amorphous 
powder  there  are  found  various  curious  but  definite  forms, 
quite  unlike  the  character  of  crystals  produced  without  the 
intervention  of  the*organic  substance. 

Mr.  Rainie  found  that  if  calcium  carbonate  be  slowly 
formed  in  a  thick  solution  of  mucilage  or  albumen  the  re¬ 
sultant  salt  is  in  the  form  of  globules,  laminated  in 
structure,  so  that  the  globules  may  be  likened  to  tiny  onions  ; 
these  globules,  when  in  contact,  becoming  agglomerated  into 
a  single  laminated  mass,  it  appearing  as  if  the  laminae  in 
immediate  apposition  blended  with  one  another.  Globular 
masses,  at  one  time  of  mulberry-like  form,  lose  the  in¬ 
dividuality  of  their  constituent  smaller  globules,  and  become 
smoothed  down  into  a  single  mass  ;  and  Mr.  Rainie  suggests 
as  an  explanation  of  the  laminated  structure  that  the  smaller 
masses  have  accumulated  in  concentric  layers  which  have 
subsequently  coalesced ;  and  in  the  substitution  of  the 
globular  for  the  amorphous  or  crystalline  form  in  the  salt 
of  lime  when  in  contact  with  various  organic  substances, 
Mr.  Rainie  claimed  to  find  the  clue  for  the  explanation  of 
the  development  of  shells,  teeth,  and  bone.  At  this  point 

p)  All  observers  are  not,  however,  agreed  as  to  the  formation  of  the 
enamel  nor  of  dentine. 


THE  DEVELOPMENT  OF  THE  TEETH. 


159 


Professor  Harting  took  up  the  investigation,  and  found  that 
other  salts  of  lime  would  behave  in  a  similar  manner,  and 
that  by  modifying  the  condition  of  the  experiment  very 
various  forms  Q)  might  be  produced.  But  the  most  im¬ 
portant  addition  to  our  knowledge  made  by  Professor 
Harting  lay  in  the  very  peculiar  constitution  of  the  “  calco- 
spherites,”  by  which  name  he  designated  the  globular  forms 
seen  and  described  by  liainie.  That  these  are  built  up  of 
concentric  laminae  like  an  onion  has  already  been  mentioned, 
and  Mr.  Bainie  was  aware  that  albumen  actually  entered 
into  the  composition  of  the  globule,  since  it  retained  its 
form  even  after  the  application  of  acid. 

But  Professor  Harting  has  shown  that  the  albumen  left 
behind  after  the  treatment  of  a  calcospherite  with  acid  is 
no  longer  ordinary  albumen ;  it  is  profoundly  modified,  and 
has  become  exceedingly  resistant  to  the  action  of  acids, 
alkalies,  and  boiling  water,  and  in  fact  resembles  chitine, 
the  substance  of  which  the  hard  skins  of  insects  consist 
rather  than  any  other  body. 

For  this  modified  albumen  he  proposes  the  name  of 
“  calcoglobulin,”  as  it  appears  that  the  lime  is  held  in  some 
sort  of  chemical  combination,  for  the  last  traces  of  lime  are 
retained  very  obstinately  when  calcoglobulin  is  submitted  to 
the  action  of  acids. 

The  “  calcospherite,”  then,  has  a  true  matrix  of  calco¬ 
globulin,  which  is  capable  of  retaining  its  form  and  structure 
after  the  removal  of  the  great  bulk  of  the  lime. 

Now  it  is  a  very  suggestive  fact  that  in  the  investigation 
of  calcification  we  constantly  meet  with  structures  remark¬ 
able  for  their  indestructibility  :  for  example,  if  we  destroy 
the  dentine  by  the  action  of  very  strong  acids,  or  by 
variously  contrived  processes  of  decalcification,  putrefaction, 
&c.,  there  remains  behind  a  tangled  mass  of  tubes,  the 

(x)  Thus  lie  was  successful  in  artificially  producing  “  dumb-bell ” 
crystals. 


160 


A  MANUAL  OF  DENTAL  ANATOMY. 


“dentinal  sheaths”  of  Neumann,  which  are  really  the 
immediate  walls  of  the  dentinal  tubes. 

Or  if  bone  be  disintegrated  by  certain  methods  there 
remain  behind  large  tubes,  found  to  be  the  linings  of  the 
Haversian  canals  (Kolliker),  and  small  rounded  bodies, 
recognisable  as  isolated  lacunae  ;  and  in  the  cuticula  dentis 
we  have  another  excellent  example  of  this  peculiarly  inde¬ 
structible  tissue. 

In  point  of  fact,  as  will  be  better  seen  after  the  develop¬ 
ment  of  the  dental  tissue  has  been  more  fully  described,  on 
the  borderland  of  calcification,  between  the  completed  fully 
calcified  tissue  and  the  formative  matrix  as  yet  unimpreg¬ 
nated  with  lime,  there  very  constantly  exists  a  stratum  of 
tissue  which  in  its  physical  and  chemical  properties  very 
much  resembles  “  calcoglobulin.” 

It  should  also  be  noted  that  globular,  spherical  forms  are 
very  constantly  to  be  seen  at  the  edges  of  the  thin  cap  of 
forming  dentine,  and  may  be  also  traced  in  and  around  the 
interglobular  spaces  (see  Fig.  35) ;  moreover,  isolated 
spherules  of  lime  salt  have  been  described  by  Messrs.  Robin 
and  Magitot  as  occurring  abundantly  in  the  young  pulps  of 
human  teeth,  as  well  as  those  in  the  herbivora,  where  their 
presence  was  noted  by  Henle  ;  perhaps  all  deposit  of  lime 
salts  commences  in  this  way. 


Calcification  of  the  Enamel. 

Although  the  calcification  of  the  dentine  commences 
before  that  of  the  enamel,  it  will  be  convenient  to  describe 
that  of  the  enamel  first,  as  being  a  somewhat  simpler  and 
more  easily  intelligible  process. 

As  has  already  been  mentioned,  I  am  distinctly  of  opinion 
that  the  enamel  is  formed  by  the  actual  conversion  of  the 
cells  of  the  enamel  organ  into  enamel,  but  as  this  view  is 


THE  DEVELOPMENT  OF  THE  TEETH . 


161 


not  held  by  all  who  have  written  upon  the  subject,  I  will 
first  mention  the  alternative  theory,  namely,  that  the  enamel 
is  in  some  sense  secreted  or  shed  out  by  these  cells.  In 
support  of  this  latter  theory  the  names  of  no  less  authoritie 
than  Professor  Huxley,  Kolliker,  Wenzel,  and  Magitot,  may 
be  adduced,  but  the  grounds  on  which  their  decisions  are 
based  are  appearances  susceptible  of  a  different  interpreta¬ 
tion.  Kolliker  considers  that  the  cells  do  not  undergo  any 
direct  conversion,  but  that  the  enamel  is  shed  out  from  the 
ends  of  the  enamel  cells,  the  enamel  fibres  therefore  corre¬ 
sponding  in  size  and  being  continuous  with  the  enamel  cells 
whence  they  were  shed  out. 

The  cells  would  thus  elaborate,  and  so  to  speak,  plaster 
on  from  their  free  ends  the  material  in  question  upon  the 
already  formed  enamel,  they  themselves  retaining  their  own 
integrity.  In  support  of  this  view  may  be  cited  the  close 
resemblance  in  the  resultant  products  in  the  case  of  enamel, 
and  of  the  shells  of  certain  mollusks,  say,  for  example,  Pinna. 
In  the  case  of  the  mollusk  the  shell  is  formed  intermittently 
by  the  margins  of  the  mantle,  which  are  closely  applied  to 
it,  but  are  at  any  time  separable,  so  that  it  is  difficult  to 
suppose  that  any  conversion  of  its  constituent  cells  can  take 
place  ;  but  it  would  rather  seem  certain  that  something 
must  be  shed  out  from  their  ends,  which  is  hardened  by  the 
deposition  in  or  with  it  of  lime  salts.  The  shell  of  Pinna 
contains  so  large  an  amount  of  organic  matter  that  its  struc¬ 
ture  is  retained  even  after  the  removal  of  the  lime  by  means 
of  an  acid,  and  it  is  conceived  that  the  cells  of  the  mantle 
are  at  work,  like  so  many  bees  plastering  wax  upon  a  honey¬ 
comb,  elaborating  and  plastering  on  their  products  so  that 
each  one  builds  on  to  its  own  prism  and  retains  for  this  its 
individuality. 

But  whether  the  enamel  cells  manufacture  something  which 
they  shed  off  from  their  ends,  or  are  themselves  converted 
into  hard  tissue  by  the  deposition  of  lime  within  their  own 


1C2 


A  MANUAL  of  dental  anatomy. 


substance,  no  one  doubts  that  they  preside  over  the  process, 
and  determine  the  form  of  the  result. 

Professor  Huxley’s  reason  for  doubting  the  direct  con¬ 
version  of  the  enamel  cells  into  enamel  was  that  a  membrane 
could  be  raised  from  the  surface  of  growing  enamel,  at  any 
period  of  its  development,  by  the  use  of  acid  reagents,  this 
membrane  necessarily  intervening  between  the  formed 
enamel  and  the  enamel  cells;  hence  he  denied  that  the 
enamel  organ  contributed  in  any  way  directly,  though  it 
might  indirectly,  to  the  development  of  the  enamel. 

To  the  nature  of  this  “  membrane  ”  I  shall  have  again  to 
refer,  so  that  for  the  present  it  will  suffice  to  say  that  the 
structure  in  question  cannot  be  demonstrated,  and  in  fact 
has  probably  no  existence,  prior  to  the  use  of  the  reagent. 

The  cells  of  the  internal  epithelium  of  the  enamel  organ 
or  enamel  cells  have  been  already  in  some  measure  de¬ 
scribed  :  they  are  elongated  cells,  forming  a  very  regular 
columnar  epithelium,  and  are  hence  rendered  hexagonal  by 
mutual  apposition  ;  they  vary  in  their  length  and  diameter 
in  different  animals. 

To  secure  uniformity  of  nomenclature,  the  name  amelo- 
blast  has  recently  been  proposed  for  them,  as  being  better 
comparable  with  the  terms  odontoblast  and  osteoblast. 

Although  they  are  connected  with  the  cells  of  the  stratum 
intermedium  by  a  process  at  their  base,  they  often  adhere 
more  strongly  to  the  enamel,  when  once  this  has  begun  to 
be  formed,  than  to  the  rest  of  the  enamel  organ,  so  that 
when  a  dental  sac  is  opened  the  enamel  cells  are  most  easily 
obtained  by  scraping  the  surface  of  the  enamel.  The  cells 
thus  torn  away  often  have  tapering  processes  at  the  ends 
directed  towards  the  enamel,  which  were  first  described  by 
my  father,  and  go  by  the  name  of  11  Tomes’  processes.”  The 
cells  are  also  slightly  enlarged  at  these  extremities,  especially 
if  they  have  been  immersed  in  glycerine  or  any  such  fluid 
which  causes  their  shrinkage,  for  this  end  of  the  cell  having 


THE  DEVELOPMENT  OF  THE  TEETH. 


163 


received  a  partial  impregnation  with,  lime  salt  at  its  peri¬ 
phery,  and  so  being  rigid,  is  unable  to  contract  with  the  rest 
of  the  cell.  These  enlarged,  everted  ends,  often  show  a  very 


sharp  contour,  their  trumpet-like  mouths  tending  to  confirm 
the  statement  of  Waldeyer  that  the  protoplasm  of  the  cell 
is  not  covered  in  by  membrane  at  its  ends.  The  ends  of  the 
enamel  cells  near  to  the  formed  enamel  are  granular,  this 
granularity  being  due  to  the  deposition  there  of  calcareous 


particles,  as  is  indicated  by  its  clearing  up  when  treated  with 
dilute  acids.  The  impregnation  with  calcareous  salts  com¬ 
mences  at  the  free  end  of  the  enamel  cell,  and  at  the  peri¬ 
phery  before  the  central  portion,  and  it  is  to  this  fact  that 
the  existence  of  “  Tomes’  processes  ”  is  due,  for  when  the 
enamel  cell  is  dragged  away  from  the  formed  enamel  prism, 
it  separates  across  the  line  of  calcification ;  and  thus  the 
axial  part  of  the  cell,  when  torn  away,  projects  out  further 


f1)  Enamel  cells  with  Tomes’  processes. 

(2)  Enamel  cells ;  the  two  on  the  right  have  been  shrunk  by  immersion 
in  glycerine,  and  present  the  open  trumpet-shaped  ends  described  in  the 

text. 

M  2 


164 


A  MANUAL  OF  DENTAL  ANATOMY. 


than  its  periphery,  in  consequence  of  calcification  having 
extended  less  far  at  this  central  portion  of  the  cell. 

In  other  words,  if  the  forming  enamel  were  freed  from  the 
adherent  enamel  cells,  its  surface  would  be  pitted,  each  little 
pit  marking  the  centre  of  an  enamel  prism  ;  and  if  a  thin 
section  of  this  immediate  surface  could  be  taken  off,  it  would 
be  pierced  with  holes  at  regular  intervals. 

The  enamel  cell  with  its  process  is  like  an  odontoblast  with 
a  very  short  dentinal  fibril,  which  has  been  pulled  out  of  the 
formed  dentine,  and  the  nature  of  the  “Tomes’  processes”  is 
well  illustrated  in  the  enamel  organs  of  marsupials.  It 
will  be  remembered  that  their  enamel  is  permeated  by  a 
large  number  of  canals,  which  become  continuous  at  the 
junction  of  the  dentine  and  enamel  with  the  dentinal  tubes. 
Accordingly  the  enamel  cell  of  a  marsupial,  engaged  in  the 
formation  of  a  permanently  tubular  enamel,  is  just  like  an 
odontoblast  in  that  it  has  a  long,  fine  process,  pulled  out  of 
the  already  formed  enamel. 

As  the  youngest  part  of  the  enamel  has  by  no  means 
attained  to  its  full  hardness,  it  is  quite  possible  to  obtain,  in 
small  pieces,  sections  parallel  to  its  surface;  the  nearer  they 
are  to  the  surface,  the  larger  will  be  the  perforations,  show¬ 
ing  what  has  already  been  stated  respecting  calcification 
commencing  at  the  periphery  of  each  cell  to  be  true.  And 
it  is  possible,  by  the  use  of  an  acid,  to  obtain  such  sections 
upon  a  larger  scale,  for  under  the  influence  of  such  a  reagent, 
this  youngest  layer  of  the  enamel  sometimes  peels  off  in  a 
sheet,  bringing  with  it  in  places  enamel  cells,  in  places 
enamel  prisms,  adhering  to  its  opposite  sides.  When 
destitute  of  adherent  enamel  cells  or  prisms,  this  so-called 
membrane  is  foraminated ;  and  the  processes  of  the  ends 
of  the  enamel  cells  are  fitted  into  and  passed  through  these 
perforations. 

The  real  nature  of  the  membrane  which  could  be  raised 
from  the  surface  of  growing  enamel  was  first  demonstrated 


THE  DEVELOPMENT  OF  THE  TEETH. 


165 


by  my  father,  and  his  explanation  has  been  accepted  by 
Waldeyer  and  other  authorities ;  it  will  be  seen  that  this 
sheet,  produced  solely  by  the  destructive  action  of  reagents, 
corresponds  with  the  membrana  preformativa  of  some  writers 
(see  page  181),  and  with  the  membrane  described  by  Pro¬ 
fessor  Huxley  as  intervening  between  the  enamel  cells  and 
the  enamel.  Hence  it  will  be  seen  that  the  fact  of  acids 
raising  a  membrane  from  the  surface  of  the  enamel  does  not 
really  militate  against  the  theory  that  the  enamel  is 
due  to  the  direct  conversion  of  the  enamel  cells  into 
enamel. 

The  cells  on  the  one  side  of  the  membrane  readily  separate 
from  one  another,  adhering,  however,  slightly  by  their 
dilated  ends  ( vide  supra),  and  the  fact  that  we  are  able  to 
isolate  the  youngest  layer  of  enamel  as  a  thin  sheet,  is 
probably  to  be  explained  by  its  chemical  nature.  It  appears 
to  belong  to  that  class  of  peculiarly  resistant  substances 
which  are  to  be  found  on  the  borders  of  calcification,  and 
behaves  very  much  like  Professor  Harting’s  “calcoglobulin” 
(see  page  15S) ;  at  all  events  it  may  safely  be  said  to  have 
undergone  some  chemical  change  preparatory  to  the  reception 
of  its  full  amount  of  lime  salts. 

The  calcification  of  the  enamel  should  be  so  complete 
that  its  fibrous  structure  is  but  slightly  apparent  in  longi¬ 
tudinal  sections,  and  the  individual  fibres  should  appear 
structureless,  with  the  exception  of  the  feebly  marked 
striation  (see  page  55).  In  enamel  of  imperfect  structural 
character  the  centre  of  the  fibre  is  not  completely  calcified, 
the  arrest  of  development  having  taken  place  short  of  its 
full  conversion. 

The  stellate  tissue  of  the  enamel  organ  disappears  long 
before  the  whole  thickness  of  the  enamel  is  formed,  and 
changes  go  on  in  the  latter  up  to  the  time  of  the  eruption 
of  the  tooth ;  the  enamel  of  a  tooth  prior  to  its  eruption 
having  a  chalky,  opaque  surface. 


166 


A  MANUAL  OF  DENTAL  ANATOMY. 


The  enamel  of  the  teeth  of  reptiles  is  developed  from  an 
enamel  organ  which  at  no  time  possesses  a  stellate  tissue ; 
this  is  also  the  case  in  all  fish  which  I  have  hitherto  ex- 


Fig.  75  t1). 

<  rl 


amined.  In  the  poison  fangs  of  snakes  the  enamel  cells, 
over  the  interior  of  the  poison  tube,  where  no  enamel  exists, 
appeared  to  be  transformed  into  a  stellate  reticulum,  which 
change  in  this  case  would  appear  to  be  a  retrograde 
metamorphosis. 

The  nuclei  of  the  enamel  cells,  which  lie  at  the  extremities 
furthest  from  the  enamel,  appear  to  recede  as  calcification 
goes  on ;  they  do  not  exercise  any  special  influence  on  the 
process  as  far  as  can  be  seen. 

P)  Transverse  section  of  the  tooth  sac  of  a  poison  fang  (Viper).  The 
crescentic  pulp  (a)  is  surrounded  by  a  layer  of  dentine  ( d ) ;  external  to 
this  is  a  layer  of  columnar  enamel  cells,  which,  upon  the  exterior  of  the 
tooth,  upon  which  a  thin  layer  of  enamel  is  to  be  formed,  are  large  con¬ 
spicuous  cells.  Where  they  pass  in  between  the  horns  of  the  crescent, 
into  that  part  which  will  ultimately  be  the  poison  canal,  their  character 
is  lost,  and  their  place  taken  by  stellate  cells  (/).  No  enamel  is  formed 
in  this  latter  position. 


THE  DEVELOPMENT  OF  THE  TEETH. 


167 


As  has  been  already  mentioned,  Kolliker  dissents  from  the  above 
account  of  the  calcification  of  the  enamel,  partly  on  the  ground 
that  enamel  cells  may  be  seen  of  the  same  size  and  form  at  all 
stages  of  the  formation  of  enamel. 

The  process  he  regards  as  one  of  secretion,  the  enamel  being  shed 
out,  so  to  speak,  from  the  free  end  of  each  enamel  cell ;  hence  the 
prisms  of  the  enamel  will  correspond  in  size  and  number  with  the 
cells  of  the  enamel  epithelium ;  the  processes  of  the  enamel  cells 
he  regards  as  being  fragments  of  this  hardened  secretion  which  are 
still  clinging  to  the  parent  cell. 

M.  Magitot  (Journal  del’Anatomie  de  M.  Ch.  Robin,  1879),  revived 
this  view,  describing  each  cell  as  terminated,  towards  the  forming 
enamel,  by  a  little  plate  of  dense  material  through  which  by  some 
process  of  exosmosis  the  constituents  of  enamel  travel  out.  He 
notes  that  these  plates  often  cohere  so  as  to  form  a  sheet  (cf.  page 
161),  but  says  nothing  of  their  being  perforated.  No  one,  however, 
who  had  seen  the  enamel  cell  of  a  marsupial  with  the  tapering 
process  five  or  six  times  as  long  as  itself  which  had  been  pulled  out 
of  the  young  enamel  would  be  satisfied  with  the  excretion  theory. 

The  reasons  for  adopting  the  opposite  view  will  have  been 
gathered  from  the  text ;  they  are,  in  brief,  the  occurrence  of  the 
“  Tomes’  processes,”  especially  in  marsupials ;  the  rigidity  of  the 
open  mouths  of  the  enamel  cells  ;  the  pitted  surface  of  the  youngest 
layer  of  enamel,  the  foraminated  membrane  which  can  be  raised 
from  it,  and  the  relation  of  these  facts  to  the  occurrence  of  the 
processes  of  the  enamel  cells. 

Schwann  believed  that  the  enamel  cell  was  constantly  increasing 
at  its  free  end  (i.e.,  that  next  to  the  enamel),  and  that  the  new 
growth,  or  youngest  part  of  the  cell,  is  calcified  as  fast  as  it  is 
formed  ;  this  view  differs  little  from  that  of  Kolliker,  who  prefers 
to  express  it  by  saying  that  this  end  of  the  cell  is  constantly  shed¬ 
ding  off  or  secreting  a  material  which  becomes  external  to  itself. 
My  father,  Waldeyer,  Hertz,,  and  many  others,  believe  that  the  cell 
growth  takes  place  not  at  this  free  end,  but  at  the  attached  nucle¬ 
ated  end,  and  that  it  is  the  oldest  portion  of  the  cell  itself  which 
receives  an  impregnation  with  salts  and  forms  the  enamel. 

Professor  Huxley’s  opinion  (page  161)  is,  I  take  it,  based  on  the 
fact  that  a  membrane  could  be  raised  from  the  surface  of  young 
enamel,  which  must  have  intervened  between  the  enamel  cells  and 
the  enamel  prisms  ;  if  my  father’s  explanation  of  the  nature  of  this 
membrane  be  accepted,  the  difficulty  vanishes. 

My  own  researches  upon  the  development  of  the  teeth  of  fishes 
also  furnish  evidence  tending  in  the  same  direction  ;  as  has  been 
already  mentioned,  the  enamel  cells  in  some  parts  of  the  enamel 
organs  of  certain  fish,  such  as  the  eel  and  perch,  and  certain 
Batrachia,  e.g .,  the  newt,  have  dimensions  very  greatly  exceeding 
those  of  the  cells  in  the  remainder  of  the  organ.  These  highly 
developed  cells,  three  times  as  long  as  the  corresponding  cells  lower 


168 


A  MANUAL  OF  DENTAL  ANATOMY. 


down  upon  the  dentine  papilla,  are  in  the  position  of  the  terminal 
cap  of  enamel  which  characterises  these  teeth.  Moreover,  in  the 
tooth  sac  of  the  poison  fang-  of  a  viper,  the  distribution  of  the  large 
cells  coincides  with  that  of  the  enamel  on  the  finished  tooth. 

Calcification  of  the  Dentine. — The  dentine  is  formed 
upon  the  surface  of  the  dentine  bulb,  or  papilla,  from  with¬ 
out  inwards,  so  that  no  portion  of  dentine  once  calcified  can 
receive  any  increase  in  external  dimensions  ;  all  additions 
must  take  place  upon  the  interior  of  the  dentine  cap.  The 
nature  of  the  dentine  bulb  has  already  been  to  some  extent 
described  ;  it  remains  to  consider  somewhat  more  minutely 
the  nature  of  its  surface.  The  cells  constituting  the  mem- 
brana  eboris,  to  which  Waldeyer  has  given  the  convenient 
name  of  “odontoblasts,”  form  an  exceedingly  sharply  defined 
layer  upon  the  surface  of  the  dentine  wall,  being  arranged 
in  a  single  row ;  the  cells  immediately  beneath  them  differ 
strongly  from  them,  so  that  there  is  not  so  marked  an 
appearance  of  transitional  structure  as  may  be  seen  in  the 
stratum  intermedium  of  the  enamel  organ.  Nothing  what¬ 
ever  like  the. linear  succession  of  formative  cells,  which,  by 
coalescence  at  their  ends  went  to  form  the  dentinal  tubes,  as 
described  by  the  older  writers,  is  to  be  seen. 

The  odontoblast  cells  vary  in  form  according  as  the  den¬ 
tine  formation  is  actively  going  on  or  not,  but  at  the  period 
of  their  greatest  activity  they  are  broad  at  the  end  directed 
towards  the  dentine  cap,  so  as  to  look  almost  abruptly 
truncated.  The  several  processes  of  the  cells  have  already 
been  described ;  there  are,  however,  sometimes  several 
“dentinal  processes”  proceeding  from  a  single  cell,  and 
Boll  has  counted  no  less  than  six. 

The  cells  are  finely  granular,  and  are,  according  to  Waldeyer 
and  Boll,  destitute  of  all  membrane ;  the  nucleus  is  oval,  lies 
in  that  extremity  of  the  cell  which  is  farthest  from  the  dentine, 
and  is  sometimes  prolonged  towards  the  dentinal  process  so 
as  to  be  ovoid  or  almost  pointed. 


THE  DEVELOPMENT  OF  THE  TEETH.  169 

The  dentinal  process  passes  into  the  tubes  of  the  dentine, 
and  it  frequently  happens  that  when  the  membrana  eboris 
is  only  slightly  separated  from  the  dentine  these  processes, 
which  constitute  the  dentinal  fibrils,  may  be  seen  stretching 
across  the  interval  in  great  numbers. 

The  odontoblasts,  as  may  be  seen  from  Figs.  31  and  77, 
are  fitted  closely  together,  and  there  is  not  much  room  for  any 
other  tissue  between  them,  so  long  as  the  formation  of  den  tine 
is  actively  going  on.  Prior  to  its  commencement,  however,  the 
cells  are  not  so  square  at  their  ends,  and  the  appearance  of 
the  thin  edge  of  such  a  pulp  suggests  the  idea  that  they  are 
bedded  in  a  transparent  and  structureless  jelly,  which  projects 
a  little  beyond  them.  To  render  my  meaning  more  clear  by 
a  homely  illustration,  the  surface  of  the  pulp  at  this  stage 
reminds  one  of  the  clear  jellies  put  upon  the  table  with 


Fig.  76  (*). 


strawberries  or  the  like  buried  in  them,  near  to,  but  beneath, 
the  surface.  But  no  such  substance  can  be  distinctly  seen 
when  once  calcification  has  actively  set  in. 

When  the  pulp  has  completed,  for  the  time  being  at  all 
events,  the  formation  of  the  dentine,  the  odontoblast  cells 
become  more  elongated  and  more  rounded  in  their  outline 
and  taper  off  towards  and  into  the  dentinal  process,  instead 
of  having  truncated  ends. 

The  cells  figured  by  Lent  as  the  formative  cells  of  dentine, 
I  regard  as  odontoblasts  taken  from  an  adult  tooth,  the 
period  of  formative  activity  being  past,  and  I  am  inclined  to 


(b  Isolated  odontoblast  cell. 


170 


A  MANUAL  OF  DENTAL  ANATOMY. 


think  that  his  views  on  the  subject  of  development  are  open 
to  criticism,  as  being  based  upon  the  appearances  presented 
by  such  old  cells. 

The  dentine  is,  I  believe,  formed  by  the  direct  conversion 
of  the  odontoblast  cells,  just  as  is  the  enamel  by  that  of  the 
enamel  cells,  and  is  derived  from  them,  and  from  them  alone. 

According  to  this  view,  which  is  supported  by  Waldeyer, 
Frey,  Boll,  Dr.  Lionel  Beale,  and  many  other  writers,  the 
dentinal  fibrils,  the  dentinal  sheaths,  and  the  matrix  between 


Fig.  77  f1). 


these  latter,  are  alike  derived  from  the  metamorphosis  of 
the  odontoblast  cell.  In  other  words,  the  three  structures 
in  question  may  be  taken  as  being  three  stages  in  the  con¬ 
version  of  one  and  the  same  substance  :  thus  we  have  the 
dentinal  fibril  in  its  soft  condition,  little  more  than  the 
unaltered  protoplasm  of  the  cell ;  then  the  dentinal  sheath, 
one  of  those  peculiarly  resistant  substances  which  lie  on  the 
borders  of  calcification;  and  lastly,  the  matrix,  the  completed, 
wholly  calcified  tissue. 

That  some  such  relation  exists  seems  to  be  indicated  by 
the  fact  that  dentinal  tubes  once  formed  are  capable  of 
further  calcification,  by  which  their  calibre  becomes  sensibly 
diminished.  Thus,  my  father  states  (speaking  of  the  incisor 


1  Odontoblasts  in  situ.  After  Waldeyer. 


THE  DEVELOPMENT  OF  THE  TEETH. 


171 


teeth  of  rodents),  “the  tubes  which  proceed  from  the  pulp 
cavity  near  the  base  of  the  tooth,  are,  in  most  cases,  per¬ 
ceptibly  larger  than  those  that  are  situated  higher  up  ; 
hence  it  follows  that,  as  the  latter  vTere  once  near  the  base 
of  the  tooth,  the  dentinal  tubes  undergo  a  diminution  of 
calibre  after  their  original  formation.  In  the  teeth  of  the 
Sciuridse  I  have  found  a  difference  of  size  amounting  to  a 
third  or  half  between  the  tubes  near  the  base  and  those 
near  the  surface  in  wear.” 

And  Dr.  Lionel  Beale  calls  attention  to  the  fact  that  the 
hollows  of  the  canals  are  largest  nearest  to  the  pulp,  and 
smallest  at  the  periphery  of  the  tooth — in  other  words,  at 
the  oldest  part ;  also  that  calcification  is  still  slowly  going 
on  even  in  advanced  life,  so  as  often  to  lead  to  the  oblite¬ 
ration  of  the  peripheral  tubes.  There  is,  too,  the  statement 
of  Robin  and  Magitot,  that  the  teeth  become  more  rich  in 
calcareous  salts  as  age  advances,  so  that  analyses  of  human 
teeth  show  great  discrepancies. 

It  is  difficult  to  see  how  a  dentinal  tube  once  formed  can 
become  contracted  to  a  third  or  half  of  its  diameter  unless 
we  believe  that  that  which  was  at  first  the  soft  tissue  (den¬ 
tinal  fibril)  occupying  its  canal  may  become  at  its  periphery 
metamorphosed  into  “  dentinal  sheath,”  while  that  which 
was  originally  this  latter  has  passed  into  the  condition  of 
matrix. 

But  it  is  quite  probable  that  the  dentinal  sheath  has  no 
separate  existence  in  the  dentine  until  after  its  disintegration 
by  a  strong  acid. 

As  I  have  elsewhere  expressed  it,  the  most  external 
portions  of  the  odontoblasts  undergo  a  metamorphosis  into 
a  gelatigenous  matrix,  which  is  the  seat  of  calcification, 
while  their  most  central  portions  remain  soft  and  unaltered 
as  the  fibrils.  Intermediate  between  the  central  perma¬ 
nently  soft  fibril  and  the  general  calcified  matrix,  is  that 
portion  which  immediately  surrounds  the  fibril,  namely,  the 


172 


A  MANUAL  OF  DENTAL  ANATOMY. 


dentinal  sheath ;  as  expressed  by  Dr.  Lionel  Beale  they  are 
protoplasm,  formed  material,  and  calcified  formed  material. 

J ust  as  in  the  case  of  enamel,  there  are  writers  who  hold  that  the 
odontoblasts  are  not  themselves  converted  into  dentine,  but  that 
they  preside  over  the  secretion  of  a  material  which  is.  Thus 
Kolliker  and  Lent  believe  that  while  the  canals  and  their  contents 
are  continuations  of  the  odontoblasts,  the  matrix  is  a  secretion 
either  from  these  cells  or  from  the  rest  of  the  pnlp,  and  so  is  an 
il  intercellular”  substance.  Their  view  is  therefore  intermediate 
between  the  excretion  and  conversion  theories  ;  and  Kolliker  goes 
on  to  say,  “  since  the  dentinal  cells  are  immediately  drawn  out  at 
their  outer  ends  into  the  dentinal  fibres,  and  do  not,  as  was  formerly 
thought,  grow  out  in  such  a  manner  that  the  dentinal  fibre  is  to  be 
regarded  only  as  the  inner  part  of  the  cell,  so  it  is  not  possible  to 
derive  the  dentine  immediately  from  the  cells.”  But  is  not  Pro¬ 
fessor  Kolliker  thinking  and  writing  of  those  aged,  spent  cells 
which  his  pupil  Lent  figured  ?  No  one  could  speak  of  a  young, 
active  odontoblast  as  “  drawn  out  into  the  dentinal  fibril.”  A  good 
section  of  young  developing  dentine  shows  that  the  cells  are  square 
and  abrupt  towards  the  dentine  ;  they  do  not  taper  into  the  dentinal 
process  in  the  smallest  degree,  and  there  is  no  room  for  any  inter¬ 
cellular  substance  whatever. 

Hertz  coincides  with  Kolliker  in  regarding  the  matrix  as  a 
“  secretion  from  all  the  dentinal  cells  in  common  which  stands  in 
no  definite  histological  relation  to  the  individual  cells,”  but  his 
figure  also  I  believe  to  be  representative  of  an  adult  inactive  surface 
of  pulp,  in  which  dentine  formation  has  almost  ceased. 

Kolliker  and  Lent  are  of  opinion  that  a  single  cell  is  sufficient  to 
form  the  whole  length  of  a  dentinal  fibril,  not  having  seen  evidence 
of  active  cell  growth  in  the  subjacent  layer  of  the  pulp,  from  which 
they  would  infer  that  the  membrana  eboris  was  supplemented  by 
new  cells  from  below.  In  a  later  edition,  however,  Kolliker  speaks 
with  much  more  hesitation  on  this  point. 

Magitot  (1881)  holds  that  the  whole  of  the  dentine  is  “a  pro¬ 
duct  elaborated  by  the  odontoblasts,”  but  neither  selected  by  nor 
formed  by  the  conversion  of  the  odontoblasts,  and  he  denies  the 
existence  of  the  sheaths  of  Neumann  in  toto. 

Klein  believes  that  the  odontoblast  forms  the  matrix  only, 
whilst  the  dentinal  fibrils  are  processes  continued  up  between  the 
odontoblasts  from  a  subjacent  layer  of  stellate  cells. 

Bobin  and  Magitot  formerly  held  that  the  dentine  matrix  was 
formed  by  the  transformation  of  the  odontoblast  cells,  but  that  the 
tubes  were  interspaces  between  these  latter,  not  corresponding  with 
the  axes  of  the  cells. 

Baume  (Odontologische  Fortschungen)  holds  that  the  odonto¬ 
blast  secrete  a  material  which  calcifies,  rather  than  that  they  are 


THE  DEVELOPMENT  OF  THE  TEETH . 


173 


themselves  converted,  and  there  are  some  appearances  which  are  still 
unexplained.  Mr.  Mummery  has  shown  to  me  sections  of  teeth  with 
the  pulps  in  situ,  which  had  been  prepared  by  impregnation  with 
previously  hardened  Canada  balsam  ;  in  these  there  appears  to  be 
something  in  the  pulp  like  a  connective  tissue  stroma — something 
which  reminds  one  of  the  connective  tissue  which  calcifies  into 
Sharpey’s  fibres  in  bone — adherent  to  the  inner  surface  of  the 
dentine.  This,  as  well  as  some  appearances  after  maceration  in 
glycerine,  described  by  Mr.  Bennett  (Odontolog.  Soc.  Transac.,  1888), 
are  as  yet  not  fully  explained,  nor  is  it  clear  how  far  they  may  be 
due  to  methods  used  in  the  preparation  of  the  specimens. 

But  it  would  appear  that  there  must  be  some  material  of  appreci¬ 
able  thickness  upon  the  inner  or  forming  surface  of  the  dentine 
which  is  not  as  yet  fully  calcified,  and  perhaps  not  in  other  respects 
as  yet  structurally  or  chemically  quite  identical  with  the  matrix 
even  when  this  latter  is  decalcified  (cf.  Fig.  78),  but  which  is  on  its 
way  towards  conversion  into  dentine  matrix. 

And  it  has  been  suggested  (Hopewell  Smith,  Dental  Record,  Aug. 
1889),  that  the  function  of  the  odontoblasts  is  purely  sensory,  a  com¬ 
parison  being  drawn  between  them  and  the  ganglion  cells  of  the 
spinal  cord,  and  that  the  work  of  elaboration  of  dentine  matrix,  &c., 
is  done  by  smaller  and  less  specialised  cells  which  lie  more  deeply 
in  the  pulp,  just  below  the  odontoblast  layer. 

Comparative  anatomy  furnishes  evidence  against  the  acceptance 
of  such  a  view,  as  many  vaso-dentines  which  contain  no  tube 
system,  and  so  no  dentinal  fibrils,  are  yet  formed  apparently  by  the 
agency  of  a  layer  of  cells  corresponding  in  most  features  with  the 
odontoblasts  of  other  creatures. 

Whilst  the  view  advocated  in  the  body  of  the  text  is  that  which 
appears  to  me  to  be  the  most  probable,  it  cannot  be  said  that  the 
question  of  dentine  calcification  is  finally  and  completely  settled  : 
there  still  remains  room  for  doubt  and  for  conjecture,  so  that  no 
dogmatic  statements  can  be  laid  down  with  safety. 

The  thinnest  layer  of  dentine,  such  as  may  be  found  at 
the  edges  of  the  dentine  cap,  is  soft  and  elastic,  and  so 
transparent  as  to  appear  structureless.  Where  it  has  at¬ 
tained  a  somewhat  greater  thickness,  globules  begin  to 
appear  in  it,  which  are  small  in  the  thinner,  and  larger  in 
the  thicker  portion  of  the  dentine  cap.  As  they  are  actually 
in  the  substance  of  the  cap,  their  growth  and  coalescence 
obviously  go  on  without  any  very  immediate  relation  to 
the  cells  of  the  pulp  ;  in  point  of  fact,  a  process  strictly 
analogous  to  that  demonstrated  by  Mr.  Rainie  and  Professor 


174 


A  MANUAL  OF  DENTAL  ANATOMY. 


Harting  (see  page  187),  is  going  on.  *  Thus  in  the  formation 
of  the  first  skin  of  dentine,  a  stage  of  metamorphosis  pre¬ 
paratory  to  impregnation  with  calcareous  salts  distinctly 
precedes  that  full  impregnation,  which  is  marked  by  the 
occurrence  of  globules  and  their  subsequent  coalescence. 
The  occurrence  of  these  globular  forms  and  consequent  large 
interglobular  spaces,  in  the  deeper  parts  of  adult  dentine,  is 
therefore  an  evidence  of  arrest  of  development  rather  than 
of  any  otherwise  abnormal  condition. 

When  the  formation  of  the  dentine  and  enamel  has  gone 
on  to  the  extent  of  the  crown  of  the  tooth  having  attained 
its  full  length,  the  reproduction  of  new  formative  pulp  (in 
teeth  of  limited  growth)  takes  place  only  over  a  contracted 
area,  so  that  a  neck,  and  finally  one  or  more  roots,  are 
the  result  of  its  conversion  into  tooth  substance.  In 
teeth  of  constant  growth,  however,  no  such  narrowing 
of  the  formative  pulp  takes  place,  but  the  additions  to 
the  base  of  the  tooth  are  of  constant,  or  ever-increasing 
dimensions,  as  is  the  case  of  some  tusks,  wThich  are  thus  of 
conical  form. 

It  is  said  that  the  number  of  roots  which  would  have  been 
developed  at  the  base  of  a  particular  dentine  organ  may  be 
inferred  from  the  vessels,  i.e.,  that  in  a  single  rooted  tooth 
the  vessels  would,  even  at  an  early  period,  form  a  single 
fasciculus,  in  a  double  rooted  one  similarly  they  would  be 
arranged  in  two  bundles,  so  that  the  ultimate  formative 
activity  will  be  exercised  around  one,  two,  or  three  centres 
of  nutrition.  I  am  not  however  able,  from  my  own  ob¬ 
servations,  to  throw  any  light  upon  this  matter. 


THE  CALCIFICATION  OF  VASO-DENTINE. 

During  the  conversion  of  the  membrana  eboris  into 
ordinary  hard  unvascular  dentine  the  vessels  of  the  formative 
pulp  recede,  so  that,  whilst  at  all  stages  a  capillary  plexus 


THE  DEVELOPMENT  OF  THE  TEETH. 


175 


is  to  be  found  just  below  the  odontoblast  layer,  no  vessels 
are  to  be  found  amongst  the  cells  which  constitute  it. 

Nevertheless  a  moment’s  reflection  will  show  that  (except 
in  the  earliest  stages,  before  any  dentine  is  formed)  the 
plexus  must  at  a  prior  time  have  occupied  the  place  now 
taken  possession  of  by  the  inward  marching  odontoblasts 
and  dentine. 

But  in  the  calcification  of  a  formative  pulp  into  vaso- 
dentine  this  recession  of  its  vessels  before  the  advancing 
border  of  calcification  does  not  take  place  ;  the  whole  vascular 
network  of  the  papilla  remains  and  continues  to  carry  blood 
circulating  through  it,  even  after  calcification  has  crept  up 
to  and  around  it. 

So  that,  if  we  imagine  a  vascular  papilla  to  have  its 
stroma  suddenly  petrified  whilst  its  circulation  went  on  all 
the  same,  we  should  have  something  like  a  vaso-dentine. 

Just  as  in  hard  dentine,  the  odontoblast  layer  is  distinctly 
marked  off  from  the  rest  of  the  dentine  organ,  and  the 
dentine  is  wholly  derived  from  its  conversion  into  calcified 
material,  so  that  the  difference  between  vaso-dentine  and 
hard  dentine  is  not  one  of  a  very  fundamental  character. 

Indeed  as  we  have  seen  (page  92),  the  same  formative 
pulp,  the  same  odontoblast  layer,  is  able  at  one  time  to  form 
hard  tubular  dentine,  at  another  vaso-dentine.  All,  therefore, 
that  has  been  before  said  of  the  calcification  of  odontoblasts 
will  apply  equally  to  those  of  a  vaso-dentine  pulp,  save  only 
that  in  the  most  typical  tissue  of  this  latter  kind  each  cell 
calcifies  solidly,  and  does  not  leave  the  axial  portion  soft,  to 
remain  as  a  dentinal  fibril. 

Of  the  development  of  Plicidentine  nothing  more  need 
be  said,  as  it  presents  no  peculiarities  which  are  not  the 
obvious  result  of  the  folding  of  the  surface  of  its  formative 

pulp. 


176 


A  MANUAL  OF  DENTAL  ANATOMY. 


THE  CALCIFICATION  OF  OSTEO-DENTINE. 

With  the  exception  of  the  thin  external  layers  (see  Fig.  48), 
which  are  developed  from  a  superficial  layer  of  not  very 
highly  specialised  cells,  osteo-dentine  is  built  up  in  a  manner 
fundamentally  different  from  that  in  which  hard  dentine, 
plicidentine,  and  vaso-dentine,  are  constructed. 

For  it  is  not,  like  these,  a  surface  formation ;  it  is  not 
laid  down  in  a  regular  manner  upon  the  exterior  of  a  pulp, 
and  it  has  no  relation  to  an  odontoblast  layer,  if  we  except 
perhaps,  its  thin  exterior  shell. 

So  soon  as  this  has  been  formed,  its  inner  surface  becomes 
roughened  by  trabeculae  shooting  inwards  into  the  substance 
of  the  pulp,  which  speedily  becomes  traversed  completely 
by  them,  as  well  as  by  the  connective  tissue  bundles  which 
are  continuous  with  them.  Thus  the  pulp,  being  pierced 
through  in  every  direction  by  these  ingrowths,  cannot  be 
withdrawn,  like  the  pulp  of  a  hard  or  of  a  vaso-dentine  tooth, 
from  the  interior  of  the  dentine  cap.  Osteoblasts  clothe, 
like  an  epithelium,  the  trabeculae  and  the  connective  tissue 
fibres  attached  to  them,  and  by  the  calcification  of  these  the 
osteodentine  is  formed. 

The  process  is  exactly  like  the  calcification  of  any  mem¬ 
brane  bone,  and  the  connective  tissue  bundles  remind  one 
of  those  which  are  believed  to  be  the  occasion  of  the 
formation  of  Sharpey’s  fibres  in  bone.  In  the  case  of  teeth 
which  are  going  to  be  ancliylosed  to  the  subjacent  bone, 
these  fibres  run  continuously  from  the  interior  of  the  dentine 
cap  down  to  the  bone,  and  calcification  in  and  around  them 
binds  the  two  inseparably  together. 

It  is  interesting  to  note,  especially  in  connection  with 
the  fact  that  some  observers  believe  Sharpey’s  fibres  to  be 
elastic,  that  the  hinged  teeth  of  the  pike  (see  Fig.  90)  owe 
their  power  of  resilience  entirely  to  the  elasticity  of  these 
connective  tissue  bundles,  which  do  not  become  completely 


THE  DEVELOPMENT  OF  THE  TEETH. 


17  7 


calcified ;  although  at  an  early  stage  it  would  be  quite  im¬ 
possible  to  say  whether  a  particular  tooth  under  observation 
was  going  to  be  anchylosed,  or  to  be  a  hinged  tooth  tied 
down  by  elastic  strings. 

The  Calcification  of  Cementum. — Just  as  is  the  case 
with  bones  elsewhere  in  the  body,  cementum  may  perhaps 
be  formed  in  two  distinct  ways,  by  membranous  ossification, 
and  by  ossification  in  a  fibro-cartilage,  the  former  method 
obtaining  upon  the  roots  of  teeth,  and  the  latter  upon  those 
crowns  where  the  cement  organ  described  by  Magitot  exists. 

At  the  time  when  the  crown  of  a  tooth  appears  through 
the  gum,  it  alone  is  complete,  and  the  root  has  yet  to  be 
calcified  ;  as  each  portion  of  dentine  of  the  root  is  completed, 
it  is  coated  with  a  closely  adherent  vascular  membrane  which 
is  in  fact  the  follicle  wall,  and  which  is  to  become,  when  the 
cement  is  formed,  the  alveolo-dental  periosteum. 

The  inner  or  dentinal  face  of  this  membrane  presents  a 
layer  of  large  cells,  the  osteoblasts  of  Gegenbaur,  and  it  is 
by  their  calcification  that  bone  or  cementum  is  directly 
formed.  These  osteoblasts  are  themselves  a  special  de¬ 
velopment  where  bone  is  about  to  be  manufactured,  as  is 
clearly  explained  in  the  following  extract  from  a  paper  by 
my  father  and  the  late  Mr.  De  Morgan,  who  termed  them 
osteal  cells  : — 

“  Here  (towards  the  bone)  in  the  place  of  cells  with 
elongated  processes,  or  cells  arranged  in  fibre-like  lines,  we 
find  cells  aggregated  into  a  mass,  and  so  closely  packed  as  to 
leave  little  room  for  intermediate  tissue.  The  cells  appear 
to  have  increased  in  size  at  the  cost  of  the  processes  which 
existed  at  an  earlier  stage,  and  formed  a  bond  of  union  be¬ 
tween  them.  Everywhere  about  growing  bone  a  careful  ex¬ 
amination  will  reveal  cells  attached  to  its  surface ,  while  the  sur¬ 
face  of  the  bone  itself  will present  a  series  of  similar  bodies  ossified. 
To  these  we  propose  to  give  the  name  of  osteal  cells.” 

Externally  to  the  osteoblast  layer,  but  still  very  near  to 


178 


A  MANUAL  OF  DENTAL  ANATOMY. 


the  perfect  cementum,  lies  a  reticulum  or  network  made  up 
of  forming  connective  tissue.  The  cells  have  largish  round 
nuclei,  and  are  each  furnished  with  three  or  four  homo¬ 
geneous  processes,  so  that  the  tissue,  save  in  very  thin  sec¬ 
tions,  looks  hopelessly  confused  from  the  interlacing  of  the 

\ 

cell  processes.  Many  of  these  processes  pass  into,  and  are  lost 
in  the  clear,  structureless  matrix  of  the  already  formed 
cementum ;  the  functions  which  they  perform  in  its  deve¬ 
lopment  are  not  very  apparent,  but  some  of  them  appear  to 
persist  in  it  as  Sharpey’s  fibres. 

Externally  to  the  fine-meshed  net-work  which  has  been 
well  figured  and  described  by  Dr.  Lionel  Beale,  the  soft 
tissue  surrounding  the  root  partakes  more  of  the  character 
of  ordinary  fibrous  tissue,  and  may  be  teased  out  into 
fibrils.  The  fibrous  bands  run  mainly  in  a  direction  from 
the  alveolus  towards  the  tooth.  Many  of  them  pass  through 
the  whole  thickness  of  the  soft  structures,  extending  from  the 
bone  of  the  alveolus  to  the  cementum  of  the  tooth,  becoming 
lost  at  each  extremity  in  the  one  tissue  or  other. 

The  osteoblasts  form  both  matrix  and  bone  corpuscles  : 
in  Professor  Klein’s  wTords  “each  osteoblast  by  the  peripheral 
portion  of  its  cell  substance  gives  origin  to  the  osseous  ground- 
substance,  wThile  the  central  protoplasm  round  the  nucleus 
persists  with  the  latter  as  the  nucleated  bone-cell.  The  bone¬ 
cell  and  the  space  in  which  it  lies  become  branched.  For 
a  row  of  osteoblasts  we  then  find  a  row  of  oblong  or  round 
territories,  each  composed  of  matrix,  and  in  it  a  nucleated 
branched  cell.  The  outlines  of  individual  territories  are 
gradually  lost,  and  we  have  then  a  continuous  osseous 
lamina,  with  its  bone-cells.  The  ground  substance  is  from 
the  outset  a  network  of  fibrils  ;  it  is  at  first  soft,  but  soon 
becomes  impregnated  with  inorganic  salts,  the  process  com¬ 
mencing  at  the  ‘point  of  ossification.’  The  bone  cells,  with 
their  processes,  are  situated  in  corresponding  lacunae  and 
canaliculi,  just  as  in  the  adult  osseous  substance.” 


THE  DEVELOPMENT  OF  THE  TEETH. 


179 


Thus  just  as  calcification  in  an  enamel  cell  or  in  an  odon¬ 
toblast  commences  upon  its  surface,  and  proceeds  inwards 
till  it  has  more  or  less  completely  pervaded  it,  so  in  the  case 
of  the  osteoblast  the  deposition  of  calcareous  salts  proceeds 
from  without  inwards.  To  use  a  rough  comparison,  we 
might  imagine  a  calcifying  osteoblast  as  like  an  egg-shell, 
the  central  cavity  of  which  was  being  gradually  obliterated 
by  the  addition  of  successive  layers  on  its  interior  (it  is  not 
to  be  understood  that  any  such  lamination  is  to  be  detected 
in  an  individual  osteoblast).  In  a  certain  number  of  osteo¬ 
blasts  this  process  of  calcification  does  not  proceed  with 
such  regularity  as  to  obliterate  their  centres,  and  at  the 


Fig.  78  0. 


same  time  to  fuse  together  their  exteriors,  but  as  it  pro¬ 
gresses  with  some  degree  of  irregularity  towards  the  centre, 
tracks  of  uncalcified  matrix  are  left,  and  finally  it  stops  short 
of  obliterating  the  central  portion  of  the  cell.  Although 
for  the  purpose  of  description  I  have  spoken  of  the  centre 
of  the  osteoblast  cell  as  a  ‘  space,’  of  course  it  is  not  hollow, 
but  consists  of  uncalcified  matrix,  and  in  this  situation  lies 
the  nucleus  of  the  cell. 

In  carmine-stained  preparations  from  the  teeth  of  calves 
a  round  nucleus  may  sometimes  be  seen  lying  in  the  stellate 


x  2 


(l)  Encapsuled  lacunas. 


180 


A  MANUAL  OF  DENTAL  ANA  TO  MV. 


“  lacuna  ;  ”  the  nucleus  soon  disappears,  and  plays  no  active 
part  in  determining  the  form  of  the  lacuna.  The  nucleus 
may  also  be  seen  in  the  developing  bones  of  human  foetuses, 
and,  though  this  is  difficult  to  understand,  the  traces  of  the 
nucleus  seem  to  be  beautifully  preserved  in  the  lacunae  of 
a  supposed  Pterodactyle  bone  from  the  Wealden,  a  section 
from  which  was  figured  by  my  father  in  the  paper  referred 
to.  Exactly  as  calcification,  advancing  with  irregularity  in 
the  interior  of  an  individual  cell,  fails  to  render  it  homo¬ 
geneous  by  pervading  its  whole  substance,  so  it  may  fail  so 
completely  to  unite  contiguous  cells  as  to  obliterate  their 
contours.  A  lacuna,  surrounded  by  such  a  contour  line, 
mapping  the  limits  of  the  original  cell,  or  cluster  of  cells,  is 
what  is  termed  an  “  encapsuled  lacuna.” 

That  which  determines  the  formation  of  a  lacuna,  or  an 
encapsuled  lacuna,  at  any  particular  spot,  is  unknown  :  all 
that  can  certainly  be  said  upon  the  subject  is  embodied  in 
the  following  extract  from  the  paper  by  my  father  and  Mr. 
De  Morgan,  above  alluded  to: — “We  see  the  boundary  of 
the  original  lacunal  cells  only  in  those  cases  where  the 
lacunae  have  but  few,  or  are  entirely  devoid  of  canaliculi. 
It  would  appear  to  be  a  law,  to  which  there  are  few,  if  any, 
exceptions,  that  when  anastomosis  is  established  between 
adjoining  lacunae,  the  lacunal  cells  blend  with  the  con¬ 
tiguous  parts,  and  are  no  longer  recognisable  as  distinct 
bodies.” 

According  to  Kolliker,  the  cementum  is  first  deposited  in 
isolated  scales,  which  coalesce  with  one  another,  rather  than 
in  a  continuous  sheet.  In  the  teeth  of  the  Primates,  the 
Carnivora,  Insectivora,  Ac.,  the  cementum,  at  least  in  any 
appreciable  thickness,  is  confined  to  the  roots  of  the  teeth. 
Various  reasons,  however,  exist,  for  regarding  Nasmyth’s 
membrane  as  an  exceedingly  thin  layer  of  cement,  which 
have  been  entered  into  in  the  section  relating  to  that 
structure,  and  need  not  be  recapitulated  here.  It  will 


THE  DEVELOPMENT  OF  THE  TEETH. 


181 


suffice  to  say,  that  it  appears  to  be  one  of  those  structures 
midway  betwixt  full  calcification  and  full  vitality,  and  shares 
with  such  substances  the  power  of  resistance  to  chemical 
reagents  which  characterises  them. 

M.  Magitot  states  that  the  calcification  of  the  cartilaginous 
cement  organ  of  Herbivora  differs  in  no  respect  from  that  of 
other  cartilages,  but  in  his  description  he  merely  states  that 
patches  of  calcification  appear  here  and  there  in  the  deepest 
portion  of  the  organ,  coalesce,  and  come  to  invade  its  entire 
thickness;  and  further  that  the  cement  at  the  period  of 
eruption  is  constituted  of  “  osteoplasts  ”  regularly  grouped 
round  vascular  canals,  and  included  in  a  ground  substance 
finely  striated.  (Journal  de  V anatomic ,  1881,  p.  32.)  Where 
intra-cartilaginous  ossifications  occur  elsewhere  in  the  body 
a  temporary  bone  is  formed  by  the  calcification  of  the 
cartilage  matrix,  which  is  subsequently  absorbed  and  swept 
away,  as  marrow- containing  channels  appear  in  it,  and  bore 
their  way  through  it,  substituting  for  the  calcified  cartilage 
a  bone  developed  from  osteoblasts,  and  ultimately  all  remains 
of  the  calcified  cartilage  or  temporary  bone  disappear.  Thus 
all  bone  whether  developed  in  cartilage  or  in  membrane 
is  formed  alike,  the  calcified  cartilage  merely  forming  a 
temporary  framework  or  scaffolding,  in  and  amongst  which 
the  bone  is  formed  from  osteoblasts.  But  M.  Magitot  does 
not  describe  in  much  detail  this  calcification  of  cartilage  and 
subsequent  removal  to  give  place  to  an  osteoblast-derived 
bone,  though  he  speaks  of  the  cartilaginous  cement  organ 
as  a  transitory  or  temporary  structure. 

Membrana  Preformativa. — To  the  student  of  dental 
development,  few  things  are  more  perplexing  than  the  con¬ 
flicting  statements  which  he  reads  in  various  works  as  to 
the  nature  and  position  of  the  Membrana  preformativa,  of 
which  I  have  hitherto  studiously  avoided  all  description  ; 
while  it  is  not  encouraging,  after  having  mastered  with 
difficulty  some  one  description  of  its  character,  to  find  that 


182 


A  MANUAL  OF  DENTAL  ANATOMY. 


many  of  the  most  recent  authors  altogether  deny  its  exist 
ence.  I  will  endeavour,  therefore,  so  far  as  I  am  able, 
although  not  myself  believing  in  its  presence,  to  put  the 
matter  in  a  clearer  light,  and  to  point  out  wherein  lie  the 
discrepancies  of  statement. 

According  to  the  older  theories  of  tooth  development, 
under  the  thrall  of  which  most  authors  have  written,  the 
tooth  germ  was  in  the  first  instance  a  free,  uncovered  papilla 
of  the  mucous  membrane,  which  subsequently  sank  in  and 
became  encapsulated,  &c.,  &c.  (see  page  121).  Moreover,  it 
was  taught  by  the  older  histologists  that  fine  homogeneous 
“  basement  membranes  ”  were  to  be  found  in  a  great  variety 
of  situations,  amongst  others  beneath  the  epithelium  of  the 
mucous  membrane,  and  that  these  were  of  (physiologically) 
much  importance,  inasmuch  as  they  formed  defining  limits, 
through  which  structures  did  not  pass.  As  a  necessary  con¬ 
sequence  of  these  views,  it  was  assumed  as  a  matter  of 
course  that  the  “dentine  papilla”  must  be  covered  over  by  a 
“basement  membrane,”  or  membrana  preformativa. 

Thus  this  membrane  necessarily  intervened  between  the 
enamel  organ  and  the  dentine  papilla,  and  hence  gave  rise 
to  difficulties  in  the  understanding  of  the  calcifying  process. 
Henle  considered  that  evidences  of  its  presence  speedily 
became  lost,  but  that  ossification  proceeded  in  opposite 
directions  upon  the  two  sides  of  this  membrane  :  from 
within  outwards  in  the  case  of  the  enamel,  from  without 
inwards  in  the  case  of  the  dentine. 

Prof.  Huxley,  starting  on  the  same  hypothesis  as  to  its 
position,  namely,  that  it  was  between  the  enamel  organ  and 
the  dentine  papilla,  came  to  a  different  conclusion  as  to  its 
after  fate  ;  relying  upon  the  fact  that  a  continuous  sheet  of 
tissue  or  membrane  can  be  raised  from  the  surface  of  the 
developing  enamel  (see  page  164),  he  concluded  that  this 
was  the  original  membrana  preformativa,  that  it  afterwards 
became  the  Nasmyth’s  membrane,  and  that  enamel  was 


THE  DEVELOPMENT  OF  THE  TEETH. 


1S3 


developed  without  the  direct  participation  of  the  enamel 
organ,  seeing  that  a  membrane  separated  the  two.  My 
reason  for  doubting  the  correctness  of  these  conclusions  has 
been  there  given ;  the  membrane  so  demonstrable  is,  I 
believe,  artificial,  and  does  not  represent  any  naturally 
existing  structure. 

Ivolliker  strongly  affirms  the  existence  of  the  membrana 
preformativa,  and  in  the  older  edition  of  his  Histology,  held 
that  it  became  converted  into  Nasmyth’s  membrane ; 
although  he  now  gives  a  different  explanation  of  the  origin 
of  Nasmyth’s  membrane,  I  have  not  found  a  definite  state¬ 
ment  as  to  his  recent  views  of  the  ultimate  fate  of  the 
membrana  preformativa. 

We  have  thus  three  situations  assigned  to  the  mem¬ 
brane  covering  the  dentine  papilla,  or  membrana  prefor¬ 
mativa. 

(i.)  Between  the  dentine  and  the  enamel  (Henle). 

(ii.)  Between  the  enamel  and  the  enamel  organ,  or  out¬ 
side  the  enamel  (Huxley). 

(iii.)  Between  the  dentine  and  the  pulp  (several  writers  of 
less  authority). 

We  come  next  to  those  writers  who  deny  its  existence 
altogether,  explaining  on  other  grounds  the  appearances 
observed. 

Markusen  believed  that  it  was  nothing  more  than  the  part 
of  the  papilla  first  ossified ;  and  Dr.  Lionel  Beale  definitely 
denies  the  existence  of  a  membrane  in  any  one  of  the  three 
situations  above  detailed,  as  do  also  Hertz,  Wenzel,  and 
Waldeyer. 

Messrs.  Robin  and  Magitot  have  offered  a  plausible  ex¬ 
planation  of  the  appearance  of  a  limiting  membrane  over 
the  pulp,  which  is  briefly  this  :  the  formative  pulp  is  rich 
in  a  clear  substance  of  gelatinous  consistency  (which  in 
fact  forms  its  chief  bulk),  and  which  reminds  the  observer 
of  the  tissue  contained  in  an  umbilical  cord.  This  is  some- 


184 


A  MANUAL  OF  DENTAL  ANATOMY. 


what  more  dense  towards  the  surface,  where  it  forms  a 
matrix  for  the  odontoblasts  and  projects  beyond  them,  so 
as  to  look,  in  section  or  at  a  thin  edge,  like  a  sort  of 
varnish  to  the  papilla.  From  its  greater  density  near  the 
surface,  it  may  become  corrugated,  and  so  look  like  a 
folded  or  torn  membrane.  I  am  quite  inclined  to  agree 
with  the  foregoing  explanation. 

I  am  inclined  to  think,  that  but  for  the  erroneous  theories 
that  the  dentine  germ  originated  as  a  free  papilla  on  the 
surface,  which  would  according  to  the  prevalent  view  have 
been  necessarily  invested  by  a  basement  membrane,  w~e 
should  never  have  heard  of  a  membrana  preformativa.  At 
all  events  it  is  difficult  to  imagine  that  such  a  membrane 
exists  upon  papilla  formed  at  such  a  great  distance  from  the 
surface  as  those  of  the  snake  or  the  lizard  (Figs.  62  and  63)  : 
and  if  there  be  such  a  membrane,  it  must  be  a  secondary 
development  upon  the  surface  of  the  mass  of  cells  which 
primarily  constitute  the  rudiment  of  the  dentine  papilla,  and 
in  that  case  is  not  a  part  of  the  general  basement  membrane 
of  the  oral  mucous  membrane ;  or  else  it  must  have  been 
carried  above  as  a  sort  of  cul  de  sac  in  front  of  the  inward 
growing  process  of  epithelium,  to  which  in  that  case  it  would 
belong  rather  than  to  the  dentine  germ.  Neither  of  these 
suppositions  commend  themselves  as  probable ;  and  a  still 
greater  obstacle  to  the  acceptance  of  a  membrane  in  this 
position  is  afforded  by  the  structure  of  Marsupial  teeth  (see 
Fig.  24),  in  which  the  membrane  would  be  everywhere  per¬ 
forated  by  the  soft  contents  of  the  dentine  and  enamel 
tubes. 


Robin  et  Magitot.  Journal  de  l’anatcmie.  1866. 

Legrcs  et  Magitot.  Follicule  Dentaire.  Journal  de  l’anatomie 

de  M.  Cli.  Robin,  1873. 

Morph ol.  du  follicule  dentaire.  1879. 
Formation  de  l’organe  dentare.  1881 
Klein.  Atlas  of  Histology.  1880. 


THE  DEVELOPMENT  OF  THE  TEETH. 


185 


Waldeyer.  Strieker’s  Histology.  1870. 

Huxley.  Quart.  Jour.  Micros.  Science.  1853. 

Kolliker.  Gewebelehre. 

Tomes,  J.  Quart.  Jour.  Micros.  Science,  1853. 

Dental  Surgery.  1859. 

Tomes,  Charles  S.  Develop,  of  Vascular  Dentine.  Philos.  Trans. 

1878. 

Develop,  of  Teeth  of  Batrachia,  Ophidia,  Se- 
lachia,  and  Teleostei.  Phil.  Trans.  1875 — 
1876. 

On  Nasmyth’s  Membrane.  Q.  J.  Microsc. 
Science,  1872. 

Owen.  Odontography.  1845. 

Anatomy  of  Vertebrates.  1870. 

Nasmyth.  Med.  Chirurg.  Transac.  1839. 

Observations  on  the  Teeth.  1835. 

Markusen.  Bulletin  de  l’Acad.  de  S.  Petersburg.  1849. 

Goodsir.  Edinburgh  Med.  and  Surg.  Journal.  1838. 

Beale,  Dr.  Lionel.  Structure  of  the  Simple  Tissues.  Archives 

of  Dentistry,  vol.  i. 

Dursy,  Emil.  Entwickelungsgeschichte  des  Kopfes.  1869. 
Hertwig.  Entwickelung  der  Placoidschuppen  und  Zahne.  Jen- 
aische  Zeitschrift.  1874. 

Zahnsystem  der  Amphibien.  Archiv.  f.  Mik.  Anat. 
1874. 

Raschkow.  Meletemata  circa  Dentium  Evolutionem.  1833. 
Heincke.  Zeitschrift  f.  Wiss.  Zool.  Bd.  xxiii.  1873. 

Wedl.  Pathologie  der  Zahne.  1870. 

Tomes  and  De  Morgan.  On  Development  of  Bone.  Phil.  Trans. 

1852. 

Gegenbaur.  Manual  of  Comparative  Anatomy.  Translated  by 
Jeffrey  Bell,  1878. 

Rollet.  Connective  Tissues,  in  Strieker’s  Histology. 

Harting.  Quart.  Journal  Micros.  Science,  1872. 

Rainie.  Brit,  and  Foreign  Med.-Chirurg.  Review.  1857. 

Dean,  M.  S.  Annotated  Translation  of  Robin  and  Magitot  on  the 
Origin  of  the  Dental  Follicle.  Chicago,  1880. 
Sudduth.  American  System  of  Dental  Surgery. 

Baume.  Odontolog.  Fortschungen. 


CHAPTER  V. 


THE  DEVELOPMENT  OF  THE  JAWS — THE  ERUPTION  AND  THE 

ATTACHMENT  OF  THE  TEETH. 

At  an  early  period  in  the  development  of  the  embryo 
there  is  a  single  primitive  buccal  cavity,  which  is  subse¬ 
quently  divided  into  a  nasal  and  an  oral  cavity  by  the 
palatine  plates  growing  horizontally  across  it ;  the  pharynx 
behind  the  hinder  end  of  the  primitive  buccal  cavity 
remains  undivided.  Both  upper  and  lower  jaws  make  their 
appearance  about  the  twentieth  day  as  little  buds  from  the 
first  visceral  arch,  and  grow  inwards  towards  the  middle 
line  :  those  which  form  the  lower  jaw  reach  to  the  middle 
and  there  coalesce,  those  for  the  upper  jaw  stop  short,  and 
the  gap  left  between  them  is  filled  by  a  double  downward 
sprouting  process  from  the  forehead,  which  afterwards  forms 
the  intermaxillary  bones.  A  failure  in  the  coalescence  of  the 
maxillary  processes  with  this  intermaxillary  process,  on  one 
or  both  sides,  results  in  a  single  or  double  hare-lip. 

In  the  lower  jaw  or  mandibular  processes  there  appears, 
about  the  end  of  the  first  month,  a  dense  cord  of  cartilaginous 
consistence,  Meckel’s  cartilage,  which  seems  to  serve  as  a 
scaffolding,  giving  form  and  consistency  to  the  lower  jaw 
prior  to  the  occurrence  of  calcification.  Meckel’s  cartilage, 
formed  as  two  distinct  halves,  soon  unites  in  the  middle,  and 
then  forms  a  continuous  curved  bar,  the  hinder  ends  of 
which  reach  up  to  the  tympanum. 

About  the  fortieth  day  a  centre  of  ossification  appears  in 


THE  DEVELOPMENT  OF  THE  JAWS. 


187 


the  mandibular  process,  which,  spreading  rapidly,  soon  forms 
a  slight  osseous  jaw  outside  Meckel’s  cartilage,  which  is  not 
however  in  any  way  implicated  in  it,  and  very  soon  begins 
to  waste  away,  so  that  by  the  end  of  the  sixth  month  it  has 
disappeared  :  that  end  of  it  alone  which  extended  up  to  the 
tympanum  does  not  so  waste  away,  but  becomes  ossified  into 
the  malleus.  There,  are,  however,  observers  who  hold  that 
in  some  animals,  at  all  events,  Meckel’s  cartilage  plays  a 
more  active  part  in  ossification  of  the  jaw. 

The  development  of  the  lower  jaw  has  been  accurately 
described  by  Mr.  Bland  Sutton  (Trans.  Odonto.  Soc.,  1883). 
After  the  appearance  of  Meckel’s  cartilage,  a  centre  of  calcifi¬ 
cation  appears  at  a  point  below  the  future  mental  foramen, 
to  which  the  name  of  the  dentary  centre  is  given  ;  then 
centres  appear  for  the  condyle,  the  coronoid  process,  the 
angle,  and,  at  the  chin,  a  mento-meckelian  centre. 

An  osseous  network  soon  connects  these,  and  a  splenial 
calcification  appears  as  a  ledge  of  bone  on  the  inner  side  of 
the  forming  jaw  immediately  above  Meckel’s  cartilage  and 
the  inferior  dental  nerve.  Upon  this  splenial  portion  the 
tooth  germs  stand  “  like  flasks  upon  a  shelf,”  then  subse¬ 
quently,  as  Meckel’s  cartilage  atrophies,  the  splenial  extends 
downwards  to  fuse  with  the  dentary,  and  so  cuts  off  the 
mylohyoid  branch  of  the  inferior  dental  nerve,  which  branch 
runs  along  the  groove  once  occupied  by  Meckel’s  cartilage. 

It  will  thus  be  seen  that  the  centres  described  by  Mr. 
Bland  Sutton  correspond  pretty  closely  with  the  several 
bones  which,  though  remaining  distinct,  together  go  to  make 
up  the  mandible  in  Sauropsida :  namely,  the  articular, 
angular,  dentary,  and  splenial  bones. 

In  the  upper  jaw  the  suture  separating  the  intermaxillary 
from  the  maxillary  bones  becomes  obliterated  very  early  on 
the  exterior  surface,  but  it  remains  long  distinguishable  on 
the  palatine  aspect  of  the  bones. 

According  to  Albrecht  the  intermaxillary  bones  are  deve- 


188 


A  MANUAL  OF  DENTAL  ANATOMY. 


loped  each  from  two  centres,  and  for  a  time  there  are 
traces  of  suture  separating  these,  so  that  he  divides 
the  inter-maxillary  bone  into  an  “  endognathion  ”  and  an 
“  exognathion.” 

The  later  changes  which  are  undergone  by  the  jaws  during 
the  development,  eruption,  and  loss  of  the  teeth,  have  long 
engaged  the  attention  of  anatomists,  and  amongst  others  of 
Hunter,  who  was  the  first  to  arrive  at  a  tolerably  correct 
appreciation  of  the  process.  In  the  first  edition  of  my 
father’s  “  Dental  Surgery,”  the  results  of  a  very  extensive 
series  of  observations  carried  out  upon  maxillse  collected  by 
himself,  were  detailed,  confirming  in  the  main  Hunter’s 
conclusions,  but  adding  many  new  points  to  our  knowledge ; 
and  from  this  work  I  have  borrowed  largely  in  the  present 
chapter.  Professor  Humphrey,  who  had  overlooked  these 
descriptions,  which  were  never  published  in  any  other  form 
than  as  an  introduction  to  the  “  Dental  Surgery,”  instituted 
a  series  of  experiments  upon  growing  animals,  which  tended 
towards  the  same  conclusions. 

As  a  means  of  giving  the  student  a  guide  in  his  reading 
of  the  following  pages,  and  a  clue  to  the  results  towards 
which  he  is  being  led,  a  preliminary  statement,  which  does 
not  pretend  to  scientific  accuracy,  may  perhaps  be  useful ; 
while  the  description  given  will  relate  for  the  most  part  to 
the  lower  jaw,  because  its  isolated  position,  bringing  it  into 
relation  with  fewer  other  bones,  renders  it  more  easy  to 
study  ;  not  that  any  difference  of  principle  underlies  the 
growth  of  the  upper  jaw.  The  different  parts  of  the  lower 
jaw  answer  for  different  purposes ;  one  division  of  its  body 
having  a  very  close  and  intimate  relation  with  the  teeth, 
the  other  serving  a  distinct  purpose,  and  being  only  secon¬ 
darily  connected  with  the  teeth. 

The  alveolar  portion  of  the  jaw,  that  which  lies  above  the 
-level  of  the  inferior  dental  canal,  is  developed  around  the  milk 
teeth  :  when  they  are  lost,  it  disappears,  to  be  re-formed 


THE  DEVELOPMENT  OF  THE  JAWS. 


189 


again  for  the  second  set  of  teeth,  and  is  finally  wholly 
removed  after  the  loss  of  the  teeth  in  old  age. 

The  portion  of  jaw  below  this  line,  which  is  essential  to 
deglutition  and  respiration,  is  late  in  acquiring  any  con¬ 
siderable  development.  Once  formed  it  is  never  removed, 
save  that  when  in  advanced  old  age  the  muscles  of  mastica¬ 
tion  are  no  longer  in  full  use,  it  becomes,  to  a  slight  extent 
only,  wasted. 

In  order  to  understand  the  drift  of  the  following  descrip¬ 
tion,  it  is  essential  to  keep  in  view  the  different  life  histories 
of  those  two  parts  of  the  jaw  just  alluded  to. 

In  an  early  foetus,  long  before  the  necessity  for  respiratory 
movement  or  deglutition  has  become  imminent,  a  thin  lamina 
of  bone  has  begun  to  be  formed  beneath  the  tooth  germs, 
forming,  as  it  were,  a  semicircular  gutter  running  round  the 
jaw,  in  which  the  developing  tooth  sacs  are  lodged.  The 
thin  gutter  of  bone  thus  formed  is  above  and  outside 
Meckel’s  cartilage,  and  intervenes  between  the  rudimentary 
inferior  maxillary  vessels  and  nerves,  and  the  teeth.  The 
sides  of  the  bony  furrow  rise  as  high  as  the  top  of  the  tooth 
germs,  but  they  do  not  arch  over  and  cover  them  in,  in  such 
manner  as  the  permanent  tooth  germs  are  arched  in,  for  the 
long  furrow  is  widely  open  at  the  top. 

Passing  on  to  the  condition  of  the  mandibles  at  the  time 
of  birth,  the  two  halves  are  as  yet  not  anchylosed,  but  are 
united  only  by  flbro-cartilage.  “  The  alveolar  margins  are 
deeply  indented  with  large  open  crypts,  more  or  less  per¬ 
fectly  formed.  The  depth  of  these  bony  cells  is  only  suffi¬ 
cient  to  contain  the  developing  teeth  and  tooth  pulps,  the 
former  rising  to  the  level  of  the  alveolar  margins  of  the 
jaws.  At  this  period  the  crypts  or  aveoli  are  not  arranged 
in  a  perfectly  uniform  line,  nor  are  they  all  equally  complete. 
The  septa,  which  divide  into  a  series  of  cells  that  which  at 
an  earlier  age  was  but  a  continuous  groove,  are  less  perfect 
at  the  back  than  at  the  front  part  of  the  mouth.  The 


190 


A  MANUAL  OF  DENTAL  ANATOMY. 


•alveoli  of  the  central  incisors  of  the  upper  and  the  lower 
jaws  are  a  little  larger  within  than  at  the  orifice,  and  this 


Fig.  79  l1). 


a 


(!)  Upper  and  lower  jaws  of  a  nine  months  foetus,  the  teeth  having 
been  removed  from  the  jaws  on  one  side  to  show  the  extent  to  which  they 
are  calcified  at  this  period.  (Two-thirds  life  size. )  a.  Alveoli  of  lateral 
incisors,  b.  Alveoli  of  canines,  c.  Alveoli  of  second  temporary  and  first 
permanent  molars.  A  bristle  has  been  passed  through  the  inferior  dental 
canal. 


THE  DEVELOPMENT  OF  THE  JAWS. 


191 


difference  is  made  still  greater  by  a  depression  upon  the  * 
lingual  wall  of  each  for  the  reception  of  the  pulp  of  the 
corresponding  permanent  tooth.  They  are  divided  from 
the  crypts  of  the  lateral  incisors  by  a  septum  which  runs 
obliquely  backwards  and  inwards  towards  the  median  line. 
The  sockets  for  the  lateral  incisors  occupy  a  position  slightly 
posterior  to  those  for  the  central  teeth,  and  are  divided  from 
the  canine  alveoli  by  a  septum  which  proceeds  obliquely 
backwards,  and  in  the  lower  jaw,  as  regards  the  median  line 
of  the  mouth,  outwards.  By  the  arrangement  of  these 
divisions,  the  alveoli  of  the  central  incisors  are  rendered 
broader  in  front  than  behind,  and  the  relative  dimensions  of 
the  sockets  of  the  lateral  teeth  are  reversed,  as  shown  in 
Fig.  79.  The  crypts  of  the  canine  teeth  are  placed  a  little 
anteriorly  to  those  of  the  laterals,  and  nearly  in  a  line  with 
those  of  the  central  incisors,  giving  to  the  jaws  a  somewhat 
flattened  anterior  aspect.” 

While  the  main  bulk  of  the  lower  jaw  is  made  up  by  the 
alveoli  of  the  teeth,  in  the  upper  jaw  the  alveoli  descend 
but  little  below  the  level  of  the  palatal  plates,  though  the 
sockets  are  tolerably  deep.  The  antrum  as  a  special  distinct 
cavity  cannot  be  said  to  exist,  being  merely  represented  by 
a  depression  upon  the  wall  of  the  nasal  cavity,  the  alveolar 
cavities  therefore  being  separated  only  by  a  thin  plate  of 
bone  from  the  orbits. 

The  figure  represents  also  the  extent  to  which  calcification 
has  advanced  in  the  various  teeth. 

A  full  half  of  the  length  of  the  crowns  of  the  central  in¬ 
cisors,  about  half  that  of  the  laterals,  and  the  tips  only  of 
the  canines  are  calcified ;  the  first  temporary  molars  are 
;  complete  as  to  their  masticating  surfaces ;  the  second  tem- 
|  porary  molars  have  their  cusps  more  or  less  irregularly 
united,  in  many  specimens  the  four  cusps  being  united  into 
a  ring  of  dentine,  the  dentine  in  the  central  depression  of 
the  crown  not  being  yet  formed.  During  the  formation  of 


192 


A  MANUAL  OF  DENTAL  AN  ATOM! 


the  permanent  teeth,  very  similar  relations  exist  between 
the  amount  of  calcification  in  the  incisors  and  canines  ;  thus 
when,  as  sometimes  happens,  the  development  of  the  teeth 
proceeds  very  imperfectly  up  to  a  certain  date,  and  then 
changes  for  the  better,  it  may  be  that  the  lower  half  of  the 
crown  of  the  central  incisor,  somewhat  less  of  the  lateral, 
and  the  extreme  tip  of  the  canine  will  be  honeycombed, 
while  the  remainder  of  the  tooth  will  be  perfect,  thus  per¬ 
petuating  an  evidence  of  the  stages  to  which  each  of  these 
teeth  had  at  that  particular  period  attained. 

Having  noted  in  some  detail  the  characters  of  the  jaws  of 
a  nine  months  foetus,  we  may  pass  on  to  the  consideration 
of  those  changes  which  precede  the  cutting  of  the  deciduous 
teeth.  A  general  increase  in  size  takes  place,  new  bone  being- 
developed  at  all  those  points  where  the  maxillee  are  con¬ 
nected  by  soft  tissue  with  other  bones,  as  well  as  from  their 
own  periosteum.  But  the  increase  in  dimensions  does  not 
take  place  in  all  directions  equally,  so  that  material  changes 
of  form  result. 

In  correspondence  with  the  elongation  of  the  tooth  sacs, 
the  alveoli  become  increased  in  depth,  and  their  edges  circle 
inwards  over  the  tooth  sacs ;  active  development  of  bone 
takes  place  in  the  sutures  uniting  the  two  halves  of  the  jaws 
to  one  another,  which  is  compensated  by  the  inclination 
imvards  of  the  alveoli  of  the  central  incisors.  In  the  lower 
jaw  the  articular  process,  at  first  hardly  raised  above  the 
level  of  the  alveolar  border,  rises  rapidly  up,  the  direction 
of  the  ramus  at  first  remaining  oblique,  though  the  angle  of 
the  jaw  becomes  developed  as  a  stout  process  for  the  attach¬ 
ment  of  muscles.  At  the  age  of  six  months  the  symphysis 
is  still  well  marked,  and  the  mental  prominence  first  becomes 
noticeable. 

An  additional  bony  crypt  for  the  first  permanent  molar 
has  also  appeared,  though  its  separation  from  that  of  the 
second  temporary  molar,  from  which  it  was  at  first  in  no  way 


THE  DEVELOPMENT  OF  THE  JA  [VS. 


193 


distinct,  is  yet  incomplete,  especially  in  the  lower  jaw.  In 
the  ujjper  jaw  the  first  permanent  molar  crypt  has  no  pos¬ 
terior  wall ;  bony  cells  for  the  permanent  central  incisors  are 
well  marked,  but  those  for  the  laterals  are  mere  deep  pits  in 
the  palatine  wall  of  the  crypts  of  the  temporary  teeth. 


Fia.  80  0). 


At  the  age  of  eight  months,  or  thereabouts,  the  process  of 
the  eruption  of  the  teeth,  or  “  teething,”  has  fairly  set  in  ; 
anchylosis  has  taken  place  at  the  symphysis  of  the  lower 
jaw,  the  mental  prominence  is  well  marked,  and  in  the 
upper  jaw  the  antrum  has  become  a  deep  depression,  extend¬ 
ing  under  the  inner  two-thirds  of  the  orbit. 

Postponing  for  the  moment  the  consideration  of  the  erup¬ 
tion  of  the  teeth,  in  order  to  follow  up  the  growth  of  the 
jaws,  it  becomes  necessary  to  take  some  fixed  points  as 
standards  from  which  to  measure  the  relative  alteration  of 
various  portions  of  the  bone.  In  most  bones,  processes  for 
the  attachment  of  muscles  would  be  very  unsuitable  for  the 
purpose,  because  they  would  alter  with  the  general  alteration 
in  the  dimensions  of  the  bone  :  thus  a  process  situated  at  a 
point  one-third  distant  from  the  articular  extremity  of  a 
long  bone,  will  still  be  found  one-third  distant  from  the  end, 
though  the  bone  has  doubled  in  length.  The  four  little 
tubercles  which  give  attachment  to  the  genio-hyo-glossus  and 
genio-hyoid  muscles  are  not,  however,  open  to  these  objec¬ 
tions,  as  they  are  already,  so  to  speak,  at  the  end  of  the 

I 

(b  Lower  jaw  of  a  nine-months  foetus. 

0 


194 


A  MANUAL  OF  DENTAL  ANATOMY. 


bone,  or,  at  least,  of  each  half  of  it ;  and  their  general  cor¬ 
respondence  in  level  with  the  inferior  dental  canal,  which  can 
hardly  be  imagined  to  undergo  much  alteration,  indicates 
that  their  position  is  tolerably  constant. 

The  points  selected  as  landmarks  are  then,  the  spinse 
mentales,  the  inferior  dental  canal  and  its  orifice,  and  the 
mental  foramen.  The  mental  foramen  itself  does  undergo 
slight  change  in  position,  but  this  change  can  easily  be 
estimated,  and  may  as  well  at  once  be  mentioned.  As  the 
jaw  undergoes  increase  in  size,  large  additions  are  made  to 
its  surface  by  deposition  of  bone  from  the  periosteum,  neces¬ 
sarily  lengthening  the  canal.  The  additions  to  the  canal 
do  not,  however,  take  place  quite  in  the  line  of  its  original 
course,  but  in  this  added  portion  it  is  bent  a  little  outwards 
and  upwards.  If  we  rasp  off  the  bone  of  an  adult  jaw  down 
to  the  level  of  this  bend,  a  j)rocess  which  nature  in  great 
part  performs  for  us  in  an  aged  jaw,  or  if  instead  we  make 
due  allowance  for  the  alteration,  the  mental  foramen  becomes 
an  available  fixed  point  for  measurement. 

The  mental  foramen,  which  undergoes  most  of  its  total 
change  of  position  within  a  few  months  after  birth,  comes  to 
correspond  with  the  centre  of  the  socket  of  the  first  tempor¬ 
ary  molar ;  later  on  it  corresponds  with  the  root  of  the  first 
bicuspid,  which  is  thus  shown  to  succeed,  in  exact  vertical 
position,  the  first  temporary  molar. 

On  the  inner  surface  of  the  jaw  the  tubercles  for  the  at¬ 
tachment  of  the  genio-hyo-glossus  and  genio-hyoid  muscles 
are  in  the  foetus,  opposite  to,  and  very  little  below,  the  base 
of  the  alveoli  of  the  central  incisors,  a  position  which  they 
afterwards  hold  with  regard  to  the  permanent  incisors.  The 
upper  of  the  two  pairs  of  processes  are  about  at  the  same 
general  level  as  the  mental  foramen. 

The  general  result  arrived  at  by  measurements  taken  from 
these  fixed  points  is  that  the  alveolar  arch  occupied  by  the 
teeth  which  have  had  deciduous  predecessors,  namely  the 


THE  DEVELOPMENT  OF  THE  JAWS. 


195 


incisors,  canines,  and  bicuspids,  correspond  very  closely  with 
the  whole  alveolar  arch  of  the  child  in  whom  the  temporary 
dentition  is  complete  ;  and  that  the  differences  wdiich  do 
exist  are  referable,  not  to  any  fundamental  alteration  in  form 
or  interstitial  growth,  but  to  mere  addition  to  its  exterior 
surface.  Or  more  briefly,  that  the  front  twenty  of  the  per¬ 
manent  succeed  vertically  to  the  places  of  the  temporary 
teeth,  the  increase  in  the  size  of  the  jaw  in  an  adult  being 
due  to  additions  at  the  back,  in  the  situation  of  the  true 
molars,  and  to  other  points  on  the  surface. 

If  measurements  be  taken  across  between  the  inner  plates 
of  the  alveoli  on  either  side  at  the  points  where  they  are 
joined  by  the  septa  between  the  first  and  second  temporary 
molars,  and  at  about  the  level  of  the  genio-hyo-glossus 
tubercles,  it  will  be  found  that  the  increase  is  slight,  if  any, 
notwithstanding  that  in  other  dimensions  there  is  a  very 
great  difference  between  the  jaws  of  a  nine-months  foetus 
and  of  a  nine-months  child. 

Again,  if  an  imaginary  line  be  stretched  across  between 
these  two  points,  and  from  its  centre  a  line  be  drawn 
forwards  to  the  spina  mentalis  in  the  same  two  jaws, 
this  will  be  found  to  differ  but  little  in  length  in  the  two 
specimens. 

But,  if  instead  of  measuring  to  the  spina  mentalis,  the 
line  had  been  carried  to  the  anterior  alveolar  plate,  a  great 
difference  would  have  been  observable ;  in  point  of  fact,  con¬ 
temporaneously  with  the  development  of  the  crypts  of  the 
permanent  teeth  inside  them,  the  temporary  teeth  and  their 
outer  alveolar  plates  are  slowly  pushed  outwards,  a  process, 
the  results  of  which  we  see  in  the  separation  which  comes 
about  between  each  one  of  the  temporary  teeth,  prior  to 
their  being  shed,  where  the  process  of  dentition  is  being 
carried  on  in  a  perfectly  normal  manner. 

Measurements  taken  for  the  sake  of  comparing  adult  jaws 
with  those  of  an  eight-months  child,  give  closely  similar 


196 


■A  MANUAL  'OF  DENTAL  ANATOMY. 


results,  which  I  have  endeavoured  to  roughly  embody  in 
the  accompanying  figures. 

In  these  it  is  shown  that  the  increase  in  the  dimensions 


Fig.  81  ('). 


of  the  jaw  has  taken  place  in  two  directions  :  by  prolonga¬ 
tion  backwards  of  its  cornua  concomitantly  with  the  addition 
at  the  back  of  the  series  of  teeth  of  the  true  molars,  which 
follow  one  another  at  considerable  intervals  ;  and  by  ad- 
ditions  to  its  exterior  surface  by  which  it  is  thickened  and 
strengthened.  The  study  of  the  growth  of  the  jaw  in 
vertical  depth  is  also  very  instructive.  We  find  that,  as 
has  already  been  mentioned,  the  history  of  that  part  of  the 
jaw  which  lies  below  the  inferior  dental  canal  is  very  different 
from  that  which  lies  above.  From  the  time  of  birth  to  that 

(b  Diagram  representing  a  jaw  of  a  nine-months  foetus,  superimposed 
upon  an  adult  jaw,  to  show  in  what  directions  increase  has  taken  place. 


THE  DEVELOPMENT  OF  THE  JAWS. 


197 


at  which  the  temporary  teeth  begin  to  be  cut,  the  jaw 
below  that  line  has  been  making  steady  but  slow  progress 
in  vertical  depth  ;  the  alveoli,  above  that  line,  have  been 
far  more  active  but  far  more  intermittent  in  their  develop¬ 
ment. 

Again,  passing  from  the  nine-months  foetus  to  the  seven- 


Fig.  82  (!). 


years-old  child,  in  whom  the  temporary  dentition  is  com¬ 
plete,  the  framework  of  the  jaw  below  our  imaginary  line  has 
attained  to  a  depth  almost  equal  to  that  which  it  is  seen  to 
have  in  an  adult ;  in  the  adult  again  it  corresponds  pretty 
well  with  that  in  an  aged  jaw.  The  alveolar  portion,  how¬ 
ever,  is  far  deeper  in  the  adult  than  in  the  child  (this 
difference  is  not  sufficiently  well  marked  in  the  figure),  and 
in  fact  constitutes  almost  the  whole  increase  in  vertical 
dimensions  down  the  passage  from  the  child’s  to  the  adult’s 
form  of  the  jaw. 

In  the  lower  jaw  we  may  take  it  as  proven  that  the 
basal  portion  has  little  relation  to  the  development  of 
the  teeth,  but  that  the  alveolar,  or  upper,  portion  is  in 
entire  and  absolute  dependence  upon  them,  a  point  to 

f1)  Lower  jaw.  The  horizontal  line  marks  the  level  of  the  inferior 
dental  canal. 


t 


precise  means  by  which  the  enlargement  of  the  jaw 
effected. 

To  a  slight  extent  there  is  formation  of  bone  going  on  a 
the  symjihjsis,  prior  to  the  complete  anchylosis  takin 

(J)  Lower  jaw  of  an  adult. 

of  (lL:^r  0f  ?,agC‘l  pers°”’  the  dotted  IiBes  indicating  the  outlin 

abS°rPtl0n’  33  thC  aSSUmCS  ^ 


-4  MANUAL  OF  DENTAL  ANATOMY. 

which  I  shall  again  return  in  speaking  of  the  eruption  of 
the  teeth. 

It  remains  to  speak  in  some  further  detail  of  the 

Fie.  83  0). 


THE  DEVELOPMENT  OF  THE  JAWS. 


199 


place  :  the  share  taken  by  this  in  increasing  the  size  of  the 
jaw  would,  however,  appear  to  be  but  small,  after  the  ter¬ 
mination  of  the  intra-uterine  period.  Additions  to  the 
surface,  at  the  edges  of  the  alveoli  and  at  the  base  of  the 
jaw,  are  continually  going  on,  and  bring  about  that  addition 
to  the  exterior  already  noticed. 

But  the  main  increase  in  the  size  of  the  jaw  has  been  in 
the  direction  of  backward  elongation ;  in  this,  as  Kdlliker 
first  pointed  out,  the  thick  articular  cartilage  plays  an  im¬ 
portant  part.  The  manner  in  which  the  jaw  is  formed 
might  also  be  described  as  wasteful ;  a  very  large  amount 
of  bone  is  formed  which  is  subsequently,  at  no  distant  date, 
removed  again  by  absorption  ;  or  we  might  compare  it  to  a 
modelling  process,  in  which  thick,  comparatively  shapeless 
masses,  are  dabbed  on  to  be  trimmed  and  pared  down  into 
form. 

To  bring  it  more  clearly  home  to  the  student’s  mind,  if 
all  the  bone  ever  formed  were  to  remain,  the  coronoid  pro¬ 
cess  would  extend  from  the  condyle  to  the  region  of  the  first 
bicuspid,  and  all  the  teeth  behind  that  would  be  buried  in 
its  base  :  there  would  be  no  “  neck  ”  beneath  the  condyle, 
but  the  internal  oblique  line  would  be  a  thick  bar,  corre¬ 
sponding  in  width  with  the  condyle.  It  is  necessary  to 
fully  realise  that  the  articular  surface  with  its  cartilage 
has  successively  occupied  every  spot  along  this  line  ;  and  as 
it  progresses  backwards  by  the  deposition  of  fresh  bone  in 
its  cartilage,  it  has  been  followed  up  by  the  process  of 
absorption  removing  all  that  was  redundant. 

On  the  outer  surface  of  the  jaw  we  can  frequently  discern 
a  slight  ridge,  extending  a  short  distance  from  the  head  of 
the  bone ;  but  if  the  prominence  were  preserved  on  the 
inner  surface,  the  inferior  dental  artery  and  nerve  would  be 
turned  out  of  their  course.  We  have  thus  a  speedy  removal 
of  the  newly-formed  bone,  so  that  a  concavity  lies  imme¬ 
diately  on  the  inner  side  of  the  condyle ;  and  microscopic 


SR  2L  Walter 


200 


A  MANUAL  OF  DENTAL  ANATOMY. 


examination  of  the  bone  at  this  point  shows  that  the  lacuna) 
of  Howship,  those  characteristic  evidences  of  absorption, 
abundantly  cover  its  surface,  showing  that  here  at  least 
absorption  is  most  actively  going  on. 

In  the  same  way  the  coronoid  process,  beneath  the  base 
of  which  the  first,  second,  and  third  molars  have  successively 
been  formed,  has  moved  backwards  by  absorption  acting  on 
its  anterior,  and  deposition  on  its  posterior  surfaces. 

The  periosteum  covering  the  back  of  the  jaw  is  also  active 
in  forming  the  angle  and  the  parts  thereabouts. 

It  is  worth  while  to  add  that  the  direction  of  growth  in 
young  jaws  is  marked  by  a  series  of  minute  ridges ;  in  like 
manner  the  characteristic  marks  of  absorption  are  to  be 
found  about  the  neck  of  the  condyle,  and  the  front  of  the 
coronoid  process,  and  those  of  active  addition  about  the  pos¬ 
terior  border,  so  that  the  above  statements  rest  upon  a  basis 
of  observation,  and  are  not  merely  theoretical.  Two  cases  of 
arrested  development  of  the  jaw  (“Dental  Surgery,”  p.  108) 
lend  a  species  of  experimental  proof  to  the  theory  of  the 
formation  and  growth  of  the  jaw  above  given. 

There  are  authors,  however,  who  maintain  that  the  growth 
of  the  jaws  is  not  merely  a  backward  elongation  of  the 
cornua,  together  with  additions  to  the  external  surface,  but 
that  an  “interstitial  growth”  takes  place. 

Wedl  inclines  to  this  latter  view,  and  the  question  cannot, 
I  think,  be  held  to  be  absolutely  settled.  Although  it  is 
difficult  to  form  any  definite  conception  of  interstitial  growth 
in  a  tissue  so  dense  and  unyielding  as  bone,  so  that  the  doc¬ 
trines  promulgated  ih  the  foregoing  pages  have  the  support 
of  a  priori  probability,  there  are  some  rather  paradoxical 
facts  to  be  met  with  in  comparative  odontology.  Never¬ 
theless,  there  can  be  no  doubt,  that  backward  elongation  as 
teeth  are  successively  added,  &c.,  is  sufficiently  near  the 
truth  in  the  case  of  human  and  most  mammalian  jaws  for 
practical  purposes.  „  ■  . . 


ERUPTION  OF  THE  TEETH 


201 


It  remains  to  notice  the  changes  in  form  which  the 
ascending  ramus  and  the  angle  of  the  jaw  undergo.  In 
the  foetus  the  ramus  is  but  little  out  of  the  line  of  the  body 
of  the  jaw,  and  the  condyle  little  raised  above  the  alveolar 
border. 

Gradually  the  line  of  development,  as  is  indicated  even  in 
the  adult  jaw  by  the  course  of  the  inferior  dental  canal,  takes 
a  more  upward  direction ;  copious  additions  of  bone  are 
made  on  the  posterior  border  and  about  the  angle,  so  that  in 
an  adult  the  ramus  ascends  nearly  at  right  angles  to  the  body 
of  the  jaw. 

In  old  age,  concomitantly  with  the  diminution  of  muscular 
energy,  the  bone  about  the  angle  wastes,  so  that  once  more 
the  ramus  appears  to  meet  the  body  at  an  obtuse  angle. 
But  all  the  changes  which  mark  an  aged  jaw  are  the  simple 
results  of  a  superficial  and  not  an  interstitial  absorption,  cor¬ 
responding  with  a  wasting  of  the  muscles,  of  the  pterygoid 
plates  of  the  sphenoid  bone,  &c. 


ERUPTION  OF  THE  TEETH. 

The  mechanism  by  which  teeth,  at  the  date  of  eruption, 
are  pushed  upwards  into  place,  is  far  from  being  perfectly 
understood.  The  simplest  theory  would  appear  to  be  that 
they  rise  up,  in  consequence  of  the  addition  of  dentine  to 
their  base  ;  in  fact  that  their  eruption  is  due  to  the  elonga¬ 
tion  of  their  fangs. 

Various  very  strong  objections  have  been  brought  forward, 
clearly  proving  that  this  cause  is  quite  inadequate  to  explain 
all  that  may  be  observed.  In  the  first  place,  teeth  with  very 
stunted  roots — which  may  be  practically  said  to  have  no 
root — are  often  erupted.  Again,  a  tooth  may  have  the 
whole  length  of  its  roots  completed,  and  yet  remain  buried 
in  the  jaw  through  half  a  person’s  life,  and  then,  late  in  life, 


202 


A  MANUAL  OF  DENTAL  ANATOMY \ 


be  erupted.  Moreover,  when  a  healthy  normal  tooth  is  being* 
erupted,  the  distance  travelled  by  its  crown  materially  ex¬ 
ceeds  the  amount  of  addition  to  the  length  of  its  roots  which 
has  gone  on  during  the  same  time. 

To  turn  to  comparative  anatomy,  the  tooth  of  a  crocodile 
moves  upwards,  tooth  pulp  and  all,  obviously  impelled  bv 
something  different  from  mere  elongation ;  and  my  own 
researches  iqoon  the  development  and  succession  of  rep¬ 
tilian  teeth  clearly  show  that  a  force  quite  independent  of 
increase  in  their  length  shifts  the  position  of,  and  “  erupts 
successive  teeth.  But  what  the  exact  nature  of  the  impulse 
may  be,  is  an  unsolved  riddle  :  the  explanations  which  I  have 
read  being,  to  my  mind,  less  satisfying  than  the  admission 
that  we  do  not  know. 

Towards  the  eighth  month  of  childhood  the  bony  crypts 
which  contain  the  temporary  teeth  in  the  front  of  the  mouth 
begin  to  be  removed.  The  process  of  absorption  goes  on 
with  greater  activity  over  the  fronts  of  the  crowns  than  over 
their  apices,  so  that  almost  the  whole  outer  wall  of  the 
alveoli  is  removed.  At  the  back  of  the  mouth  the  crypts 
still  retain  their  inverted  edges  ;  indeed,  development  of  the 
crypts  is  still  going  on  in  this  part  of  the  mouth. 

When  a  tooth  is  about  to  be  cut,  very  active  absorption  of 
its  bony  surroundings  goes  on,  particularly  on  the  anterior 
surface,  the  bone  behind  it  being  still  required  as  forming- 
part  of  the  crypt  of  the  developing  successional  tooth.  But 
no  sooner  has  the  crown  passed  up  through  the  very  wide 
and  free  orifice  so  formed,  than  absorption  gives  place  to 
deposition,  and  the  bone  rapidly  developes  so  as  to  loosely  ‘ 
embrace  the  neck  of  the  tooth. 

Additions  to  the  margin  of  the  alveoli  keep  pace  with 
the  gradual  elongation  of  the  roots  of  the  teeth  ;  as  this  is 
a  moderately  rapid  process,  the  alveolar  portion  of  the  jaw 
increases  in  depth  almost  abruptly. 

But  it  does  not  do  so  uniformly  all  over  the  mouth  ;  if  it 


ERUPT  10  X  OF  THE  TEETH. 


203 


did,  the  teeth  could  only  he  closed  at  the  back  of  the  mouth, 
unless  the  rami  elongated  by  an  equally  sudden  accession  of 
new  bone. 

The  front  teeth  are  erupted  first,  and  the  jaw  deepens 
first  in  front :  later  on  the  back  teeth  come  up  and  the  jaw 

Fig.  85  (J). 


is  deepened  posteriorly  ;  meanwhile  the  elongation  of  the 
rami  has  been  going  on  slowly,  but  'without  interruption. 
Thus  is  brought  about  a  condition  of  parts  allowing  of 
the  whole  series  of  teeth  coming  into  their  proper  mutual 
antagonism. 

It  was  pointed  out  by  Trousseau  that  the  eruption  of  the 
teeth  is  not  a  continuous  process,  which,  once  commenced,  is 
carried  on  without  intermission  to  its  completion,  but  that  it 

O  Jaws  of  a  male  nine  months  old,  in  which  the  eruption  of  the  teeth 
is  just  commencing. 


204 


A  MANUAL  OF  DENTAL  ANATOMY, 


is  interrupted  by  periods  of  repose.  The  teeth  are,  according 
to  his  statement,  cut  in  groups  ;  the  eruption  of  the  teeth  of 
each  group  being  rapid,  and  being  succeeded  by  a  complete 
cessation  of  the  process.  Individual  variations  are  nume¬ 
rous  ;  the  following  may  be  taken  as  an  approximation  to 
the  truth  :  — 

The  lower  centrals  are  erupted  at  an  age  ranging  from  six 
to  nine  months ;  their  eruption  is  rapid,  and  is  completed  in 
ten  days  or  thereabouts ;  then  follows  a  rest  of  two  or  three 
months. 

Next  come  the  four  upper  incisors ;  a  rest  of  a  few 
months ;  the  lower  laterals  and  the  four  first  molars  ;  then 
a  rest  of  four  or  five  months. 

The  canines  are  peculiar  in  being  the  only  teeth  of  the 
temporary  set  which  come  down  between  teeth  already  in 
place.  To  this,  as  well  as  to  the  greater  length  of  their 
root  (though  it  is  not  quite  clear  what  this  has  to  do  with 
it),  Trousseau  ascribes  the  great  length  of  time  which  their 
eruption  occupies,  it  taking  two  or  three  months  for  its  com¬ 
pletion.  According  to  him,  children  suffer  more  severely 
from  constitutional  disturbance  during  the  cutting  of  these 
teeth  than  that  of  any  other,  but  Dr.  West  thinks  that  the 
eruption  of  the  first  molars  causes  the  most  suffering.  It 
may  also  be  noted  that  the  canines  during  their  develop¬ 
ment  lie  farther  from  the  alveolar  border  than  do  the  other 
teeth,  so  that  they  travel  a  greater  distance ;  obviously,  not 
merely  from  the  elongation  of  the  root,  which  is  wdiolly 
inadequate  to  effect  such  a  change  in  position. 

The  dates  of  the  eruption  of  the  milk  teeth  vary  much, 
no  two  authors  giving  them  alike  ;  but  the  wdiole  of  the 
deciduous  teeth  are  usually  cut  by  the  completion  of  the 
second  year.  Cases  in  which  incisors  have  been  erupted 
before  birth  are  not  very  uncommon.  At  a  time  when  the 
crowns  of  all  the  deciduous  teeth  have  been  fully  erupted, 
their  roots  are  still  incomplete,  and  are  widely  open  at  their 


ERUPTION  OF  THE  TEETH. 


r 


£0.5 


basis,  so  that  it  is  not  till  between  the  fourth  and  sixth 
years  that  the  temporary  set  of  teeth  can  be  called  abso¬ 
lutely  complete. 

At  the  sixth  year,  preparatory  to  the  appearance  of  any 


Fig.  86  (A 


of  the  permanent  teeth,  the  temporary  teeth  may  be  observed 
to  be  slightly  separated  from  each  other ;  they  have  come  to 
occupy  a  more  anterior  position,  pushed  forward,  it  may  be, 

•  by  the  great  increase  in  size  of  the  crypt  of  the  permanent 
teeth  behind  them.  The  general  relation  of  these  to  the 
temporary  teeth  may  be  gathered  from  the  accompanying 
figure,  in  which  it  will  be  noticed  that  the  canines  lie  far 
above  and  altogether  out  of  the  line  of  the  other  teeth,  and 
that  a  slight  degree  of  overlapping  of  the  edges  of  the  per¬ 
manent  central  and  lateral  incisors  exists. 

The  bicuspids  lie  in  bony  cells  which  are  embraced  pretty- 
closely  by  the  roots  of  the  tempor  iry  molars,  and  it  hence 

(!)  Normal  well-formed  jaws,  from  which  the  alveolar  plate  has  been  in 
great  part  removed,  so  as  to  expose  the  developing  permanent  teeth  in 
their  crypts  in  the  jaws. 


206 


A  MANUAL  OF  DENTAL  ANATOMY. 


happens  that  extraction  of  the  latter  sometimes  brings  them 
away  in  their  entirety. 

The  first  permanent  molars  are  erupted  in  a  manner  closely 
similar  to  that  described  as  occurring  with  the  temporary 
teeth  ;  that  is  to  say,  their  bony  crypts  become  widely 
opened  out  by  absorption,  the  crown  passes  out,  and  new 
bone  is  rapidly  formed  which  embraces  the  neck,  prior  to 
any  considerable  length  of  root  being  formed. 

Last,  then,  follows  the  absorption  of  the  root  of  the  tem¬ 
porary  teeth,  a  matter  first  accurately  investigated  by  my 
father.  The  root  at  or  near  to  its  end,  becomes  excavated 
by  shallow  cup-shaped  depressions ;  these  deepen,  coalesce, 
and  thus  gradually  the  whole  is  eaten  away.  Although  ab¬ 
sorption  usually  commences  on  that  side  of  the  root  which 
is  nearest  to  the  successional  tooth,  it  by  no  means  invari¬ 
ably  does  so ;  it  may  be,  and  often  is,  attacked  on  the  oppo¬ 
site  side,  and  in  many  places  at  once. 

The  cementum  is  usually  attacked  first,  but  eventually 
dentine,  and  even  enamel,  come  to  be  scooped  out  and 
removed  by  an  extension  of  the  process.  That  part  of  the 
dentine,  however,  which  immediately  surrounds  the  pulp 
appears  to  have  more  power  of  resistance  than  any  other 
part  of  the  tooth,  and  thus  often  persists  for  a  time  as  a  sort 
of  hollow  column.  The  absorption  of  the  temporary  teeth 
is  absolutely  independent  of  pressure  ;  the  varying  position 
of  the  excavation  has  already  been  noticed,  and  it  may  be 
added  that  in  many  lower  animals,  for  example,  the  frog  or 
the  crocodile,  the  growing  tooth  sac  passes  bodily  into  the 
excavation  made  before  it  in  the  base  of  the  tooth  which  has 
preceded  it,  while  if  pressure  had  had  any  share  in  the  matter 
the  cells  of  its  enamel  organ,  Ac.,  must  have  inevitably  been 
crushed  and  destroyed. 

Again,  when  the  absorption  and  shedding  of  the  first  teeth 
have  taken  place  early,  before  their  successors  are  ready  to 
appear,  perfect  little  sockets  are  formed  behind  the  lost 


ERUPTION  OF  THE  TEETH. 


207 


temporary  teeth,  cutting  them  off  from  the  permanent  teeth 
destined  to  follow  them.  Absorption,  too,  may  attack  the 
roots  of  permanent  teeth,  which  is  another  reason  for  regard-. 

Fig.  87  ([). 


ing  the  process  as  not  necessarily  dependent  upon  the 
approach  of  a  displacing  tooth.  Closely  applied  to  the  ex¬ 
cavation  produced  by  absorption  is  a  mass  of  very  vascular 
soft  tissue,  the  so-called  absorbent  organ.  The  surface  of 

(l)  Jaws  of  a  six-year-old  child.  In  the  upper  jaw  complete  sockets  are 
seen  where  the  temporary  incisors  have  been  shed. 


A  MANUAL  OF  DENTAL  ANATOMY. 


208 


this  is,  composed  of  very  large  peculiaivlooking  cells,  bearing 
some  little  resemblance  to  those  known  as  “  myeloid  cells,” 
or  the  “giant  cells”  of  recent  authors.  Microscopic  ex¬ 
amination  of  the  excavated  surface  shows  it  to  be  covered 
with  small  hemispherical  indentations,  the  “lacunae  of  How- 
ship,”  into  each  of  which  one  of  the  giant  cells  fitted,  and  in 
which  they  may  sometimes  be  seen  in  situ. 

In  what  manner  these  giant  cells,  or  “  osteoclasts,”  effect 
their  work  is  not  known,  but  their  presence  where  absorption 
of  hard  tissues  is  going  on  is  universal.  Some  suppose  that 
they  put  forth  amoebiform  processes,  others  that  they  secrete 
an  acid  fluid,  but  nothing  very  definite  is  known ;  a  curious 
parallel  is  afforded  by  the  manner  in  which  a  fungus  can 
drill  and  tunnel  through  and  through  the  dentine,  as  may  be 
very  constantly  observed  in  teeth  long  buried. 

The  process  of  absorption  once  commenced  does  not  neces¬ 
sarily  proceed  without  intermission,  but  may  give  place  for 
a  time  to  actual  deposition  of  osseous  tissue  on  the  very  sur¬ 
face  eroded  ;  probably  by  the  agency  of  the  absorbent  cells 
themselves,  which  are  capable  of  being  calcified  in  the  exca¬ 
vations  they  have  individually  made. 

These  alternations  of  absorption  and  deposition,  so  com¬ 
mon  a  result  of  inflammations  of  the  pulp,  or  of  the  alveolo- 
dental  periosteum,  as  to  be  diagnostic  of  the  former  occurrence 
of  these  maladies,  often  occur  during  the  normal  process  of 
the  removal  of  the  deciduous  teeth,  and  result  in  the  deposi¬ 
tion  of  a  tissue  not  unlike  cementum  in  excavations  made 
in  the  dentine,  or  even  in  the  enamel. 

The  eruption  of  the  permanent  teeth  is  a  process  closely 
analogous  to  that  of  the  temporary  set.  Rapid  absorption 
of  the  bone,  especially  on  the  exterior  surface  of  the  crypts, 
takes  place,  and  an  orifice  very  much  larger  than  the  crown 
of  the  tooth  is  quickly  opened  out. 

Hence  it  is  that  the  slightest  force  will  suffice  to  determine 
the  direction  assumed  by  the  rising  crown  :  a  fragment  of  a 


ERUPTION  OF  THE  TEETH. 


209 


root  of  a  temporary  tooth,  the  action  of  the  lips  and  tongue, ' 
&c.,  are  all  potent  agencies  in  modifying  the  arrangement  of 
the  tedth. 

The  temporary  teeth  stood  vertically,  the  permanent 
teeth  in  front  of  the  month  stand  obliquely,  thus  opening 
a  space  between  the  lateral  incisors  and  the  first  bicuspid 
for  the  canine,  which  during  development  was  out  of  the 
line  altogether.  And,  inasmuch  as  the  crowns  of  the  teeth 
are  on  the  whole  much  larger  than  their  necks,  it  would 
be  manifestly  impossible  for  them  all  to  come  down  simul¬ 
taneously. 

The  permanent  teeth  usually  make  their  appearance  in 
the  following  order  : — First  permanent  molars,  about  the 
seventh  year  ;  a  little  later,  the  lower  central  incisors,  upper 
centrals  and  laterals,  the  first  bicuspids,  the  canines,  the 
second  bicuspids,  the  second  permanent  molars,  the  third 
permanent  molars. 

The  period  of  eruption  is  variable.  From  a  comparison 
of  several  tables,  I  find  the  principal  discrepancies  to  relate 
to  the  date  of  the  appearance  of  the  canines  and  the  second 
bicuspids.  The  canine  would  certainly  appear  to  belong  to 
the  eleventh  and  twelfth  years ;  but  some  authors  consider 
that  the  second  bicuspid  is  usually  cut  earlier,  others  later 
than  this  date. 

We  may  now  revert  to  the  phenomena  observed  in  the 
alveolar  processes.  They  were  first  built  up  as  crypts  with 
overhanging  edges  enclosing  the  temporary  teeth  :  then  they 
were  swept  away,  in  great  part,  to  allow  of  the  eruption  of 
the  temporary  teeth  ;  and  next  they  were  rebuilt  about  their 
necks,  to  form  their  sockets. 

Once  more,  at  the  fall  of  the  deciduous  teeth,  the  alveoli 
are  swept  away,  the  crypts  of  the  permanent  teeth  are 
widely  opened,  and  the  permanent  teeth  come  down  through 
the  gaping  orifices. 

When  they  have  done  so,  the  bone  is  reformed  so  as  to 


210 


A  MANUAL  OF  DENTAL  ANATOMY. 


closely  embrace  their  necks,  and  this  at  a  period  when  but 
little  of  the  root  has  been  completed. 

Take  for  example  the  first  upper  or  lower  molars  :  their 
short  and  widely  open  roots  occupy  the  whole  depth  of  the 
sockets,  and  reach  respectively  nearly  to  the  floor  of  the 
antrum  and  the  inferior  dental  canal.  No  growth,  there¬ 
fore,  can  possibly  take  place  in  these  directions  ;  the  utmost 
available  depth  has  already  been  reached,  and  as  the  roots 
lengthen  the  sockets  must  be  deepened  by  additions  to  their 
free  edges. 

It  is  impossible  to  insist  too  strongly  upon  this  fact,  that 
the  sockets  grow  up  with  and  are  moulded  around  the  teeth 
as  the  latter  elongate.  Teeth  do  not  come  down  and  take 
possession  of  sockets  more  or  less  ready  made  and  pre¬ 
existent,  but  the  socket  is  subservient  to  the  position  of  the 
tooth ;  wherever  the  tooth  may  chance  to  get  to,  there  its 
socket  will  be  built  up  round  it. 

Upon  the  proper  appreciation  of  this  fact  depends  our 
whole  understanding  of  the  mechanism  of  teething ;  the 
position  of  the  teeth  determines  that  of  the  sockets,  and  the 
form  of  the  pre-existent  alveolar  bone  has  little  or  nothing 
to  do  with  the  disposition  of  the  teeth. 

During  the  period  of  eruption  of  the  permanent  teeth  the 
level  of  the  alveolar  margin  is  seen,  in  a  dried  skull,  to  be 
extremely  irregular,  the  edges  of  the  sockets  corresponding  to 
the  necks  of  the  teeth,  whether  they  have  attained  to  their 
ultimate  level,  or  have  been  but  just  cut. 

And  when  temporary  teeth  have  been  retained  for  a  longer 
period  than  is  natural,  they  sometimes  become  elevated  to 
the  general  level  of  the  permanent  teeth  (which  is  consider¬ 
ably  higher  than  that  of  the  temporary  teeth),  so  that  they 
take  their  share  of  work  in  mastication.  When  this  is  the 
case  the  alveoli  are  developed  round  them,  and  come  to 
occupy  with  their  tooth  a  higher  level  than  before. 

Enough  has  perhaps  been  said  to  illustrate  the  entire 


ERUPTION  OF  THE  TEETH . 


211 


dependence  of  the  alveoli  upon  the  teeth,  a  relation  of  which 
dentists  every  day  avail  themselves  in  the  treatment  of 
regulation  cases :  it  remains  to  sav  a  few  words  as  to  the 
forces  which  do  determine  the  position  of  the  teeth. 

Inasmuch  as  when  a  tooth  leaves  its  bony  crypt,  the  bone 

Fig.  88  (J). 


does  not  at  first  closely  embrace  it,  but  its  socket  is  much 
too  large  for  it,  a  very  small  force  is  sufficient  to  deflect  it. 
And,  indeed,  a  very  slight  force,  constantly  operating,  is 
sufficient  to  materially  alter  the  position  of  a  tooth,  even 
when  it  has  attained  to  its  full  length. 

Along  the  outside  of  the  alveolar  arch  the  muscular  lips 
are  exercising  a  very  symmetrical  and  even  pressure  upon 
the  crowns  of  the  teeth ;  so  also  the  tongue,  with  equal 
symmetry,  is  pushing  them  outwards  :  between  the  two  forces, 


f1)  From  a  child  aged  fourteen.  The  specimen  well  exemplifies  the  fact 
that  tlie  height  of  the  alveolar  edge  corresponds  exactly  to  the  position  of 
the  neck  of  each  tooth,  on  which  it  is  wholly  dependent.  A  temporary 
tooth  (the  first  right  lower  temporary  molar)  has  been  elevated,  so  that  it 
has  attained  to  the  level  of  the  surrounding  permanent  teeth,  and  the  edge 
of  the  socket  follows  the  level  of  the  neck  of  the  tooth. 

r  2 


212 


A  MANUAL  OF  DENTAL  ANATOMY. 


the  lips  and  the  tongue,  the  teeth  naturally  become  moulded 
into  a  symmetrical  arch.  That  the  lips  and  tongue  are  the 
agencies  which  mainly  model  the  arch  is  very  well  illustrated 
by  that  which  happens  in  persons  who  have  from  childhood 
suffered  from  enlargement  of  the  tonsils,  or  from  adenoid 
growths  in  the  pharynx,  and  are  consequently  obliged  to 
breathe  through  an  open  mouth.  This  causes  a  slight 
increase  in  the  tension  of  the  lips  at  the  corners  of  the 
mouth,  and  is  impressed  upon  the  alveolar  arch  as  an 
inward  bending  of  the  bicuspids  at  that  point ;  thus  persons 
with  enlarged  tonsils  will  be  found,  almost  invariably,  to 
present  one  of  the  forms  of  mouth  known  as  V-shaped. 

But  Dr.  Norman  Kingsley  attaches  far  more  importance 
to  disturbed  innervation  than  to  any  mechanical  causes,  and 
refers  most  dental  irregularities  to  unhealthy  conditions  of 
the  child’s  nervous  system. 

When  the  crowns  of  the  teeth  have  attained  such  a  level 
as  to  come  in  contact  with  their  opposing  teeth,  they  very 
speedily,  from  readily  intelligible  mechanical  causes,  are 
forced  into  a  position  of  perfect  correspondence  and  an¬ 
tagonism  ;  and  even  at  a  somewhat  later  period  than  that  of 
eruption,  if  this  antagonism  be  interfered  with,  the  teeth  will 
often  rise  up  so  as  to  readjust  themselves  in  this  respect. 

The  roots  of  the  central  incisor  teeth  are  completed  at 
about  the  tenth  year,  the  laterals  a  little  later. 

The  canines  are  not  quite  complete  at  the  twelfth  year,  but 
both  first  and  second  bicuspids  are. 

The  first  permanent  molar  is  completed  between  the  ninth 
and  tenth  year. 

The  second  permanent  molar  between  the  sixteenth  and 
seventeenth  year. 

The  third  between  the  eighteenth  and  twentieth. 

These  data  are  taken  from  a  paper  by  Dr.  Pierce  ( Dental 
Cosmos ,  1884). 


THE  ATTACHMENT  OF  TEETH. 


213 


THE  ATTACHMENT  OF  TEETH. 

Although  the  various  methods  by  which  teeth  are  fixed  in 
their  position  upon  the  bones  which  carry  them  pass  by 
gradational  forms  into  one  another,  so  that  a  simple  and  at 
the  same  time  absolutely  correct  classification  is  impossible, 
yet  for  the  purposes  of  description  four  principal  methods 
may  be  enumerated,  namely,  attachment  by  means  of  fibrous 
membrane,  by  a  hinge,  by  anchylosis,  and  by  implantation 
in  bony  sockets. 

Attachment  by  means  of  Fibrous  Membrane. — An 

excellent  illustration  of  this  manner  of  implantation  is 
afforded  by  the  Sharks  and  Rays,  in  which  the  teeth  have 
no  direct  connection  with  the  cartilaginous,  more  or  less 
calcified,  jaws,  but  are  embedded  solely  in  the  tough  fibrous 
mucous  membrane  which  covers  them.  This,  carrying  with 
it  the  teeth,  makes  a  sort  of  sliding  progress  over  the  curved 
surface  of  the  jaw,  so  that  the  teeth  once  situated  at  the 
inner  and  lower  border  of  the  jaw,  where  fresh  ones  are 
constantly  being  developed,  rotate  over  it,  and  come  to 
occupy  the  topmost  position  (cf.  description  of  the  denti¬ 
tion  of  the  sharks).  That  the  whole  fibrous  gum,  with  the 
attached  teeth,  does  really  so  slide  over  the  surface  of  the 
jaw,  was  accidentally  demonstrated  by  the  result  of  an 
injury,  which  had  been  inflicted  upon  the  jaws  of  a  shark. 

The  fibrous  bands  by  which  each  individual  tooth  of  the 
shark  is  bound  down  are  merely  portions  of  that  same  sheet 
of  mucous  membrane  which  furnished  the  dentine  papillae  ; 
and  the  gradual  assumption  of  the  fibrillated  structure  by 
that  portion  of  the  mucous  membrane  which  is  contiguous 
to  the  base  of  the  dentine  papilla  may  be  traced,  no  such 
fibrous  tissue  being  found  at  the  base  of  young  papillae,  and 
very  dense  bands  being  attached  to  the  bases  of  the  com- 
pleted  calcified  teeth. 


214 


A  MANUAL  OF  DENTAL  ANATOMY. 


A  large  number  of  fisli  have  their  teeth  attached  to  short 
pedestals  of  bone  by  means  of  a  sort  of  annular  ligament, 
which  allows  of  a  slight  degree  of  mobility. 

By  the  limitation  of  this  ligament  to  one  side,  where  it  is 
greatly  strengthened,  we  pass  by  easy  transitions  to  those 
more  specialised  arrangements  characteristic  of  hinged 
teeth. 

Attachment  by  an  Elastic  Hinge. — The  possession 
of  moveable  teeth,  able  to  yield  to  pressure  and  subsequently 
to  resume  the  upright  position,  was  formerly  supposed  to  be 
confined  to  the  Lophius  (Angler)  and  its  immediate  allies. 
I  have  however  found  hinges  in  the  common  Pike  (Esox), 
and  in  the  Gadidse  (Cod  tribe) ;  so  that,  as  they  occur  in 
these  fish  so  widely  removed  from  one  another  in  other 
respects,  it  is  probable  that  further  investigation  will  bring, 
and  indeed  is  bringing,  to  light  many  other  examples  of 
this  very  peculiar  method  of  attachment,  eminently 
suited  to,  and  hitherto  only  discovered  in,  fish  of  predatory 
habits. 

In  the  Angler,  which  obtains  its  food  by  lying  in  ambush 
on  the  bottom,  to  which  it  is  closely  assimilated  in  colour, 
many  of  the  largest  teeth  are  so  hinged  that  they  readily 
allow  an  object  to  pass  into  the  mouth,  but  rebounding 
again,  oppose  its  egress.  These  teeth  are  held  in  position 
by  dense  fibrous  ligaments  radiating  from  the  posterior  side 
of  their  bases  on  to  the  subjacent  bone,  while  the  fronts  of  the 
bases  of  the  teeth  are  free,  and,  when  the  teeth  are  pressed 
towards  the  throat,  rise  away  from  the  bone.  The  elasticity 
of  the  ligament  is  such  that  when  it  has  been  compressed 
by  the  tooth  bending  over  towards  it,  the  tooth  returns  it 
instantly  into  position  with  a  snap.  Many  of  the  teeth  of 
the  Angler  are,  like  most  fishes’  teeth,  anchylosed  firmly. 

The  Hake  (Merlucius,  one  of  the  Gadidm)  possesses  two 
rows  of  teeth,  the  inner  and  shorter  of  which  are  anchylosed, 
whilst  the  outer  and  longer  are  hinged. 


THE  ATTACHMENT  OF  TEETH. 


215 


In  some  respects  these  hinged  teeth  are  more  highly 
specialised  than  those  of  the  Angler,  which  they  resemble  in 
being  attached  by  an  elastic  hinge  fixed  to  their  inner  sides, 

Fig.  89  (*). 


the  elasticity  of  which  is  brought  into  play  by  its  being  com¬ 
pressed,  or  at  all  events  bent  over,  upon  itself. 

The  pulp  is  highly  vascular,  and  its  vessels  are  so  arranged 
that,  by  entering  the  pulp  through  a  hole  in  the  ligament, 

(b  Hinged  tooth  of  Hake.  a.  Vaso  dentine.  5.  Pulp.  c.  Elastic 
hinge,  d.  Buttress  of  bone  to  receive  /,  formed  out  of  bone  of  attach¬ 
ment.  e.  Bone  of  jaw.  /.  Thickened  base  of  tooth,  g.  Enamel  tip. 


216 


A  MANUAL  OF  DENTAL  ANATOMY. 


which  is  about  at  the  axis  of  motion,  they  escape  being 
stretched  or  torn  during  the  movements  of  the  tooth. 
But  the  base  of  the  tooth  itself  is  modified  so  as  to  be 
particularly  fitted  for  resisting  the  jars  to  which  a  moveable 
tooth  must  at  times  be  exposed,  and  so  is  the  bone  upon 
which  it  is  set. 

As  is  seen  in  the  figure,  the  base  of  the  tooth,  on  the  side 
opposite  to  the  hinge,  is  thickened  and  rounded,  the  advan¬ 
tages  which  such  a  form  must  possess  over  a  thin  edge  when 
bumping  upon  the  bone  being  sufficiently  obvious.  This 
thickened  edge  is  received  upon  a  little  buttress  of  bone,  and 
it  occupies  a  much  higher  level  than  the  oj)posite  thin  edge 
to  which  the  hinge  is  attached,  so  that  the  tooth  cannot  pos¬ 
sibly  be  bent  outwards  without  actual  rupture  of  the  ligament. 

And  what  is  not  a  little  remarkable  is,  that  whilst  the 
Hake,  the  most  predatory  of  all  the  Gadidae,  is  possessed  of 
these  very  perfectly  hinged  teeth,  other  members  of  the 
family  have  teeth  moveable  in  a  less  degree,  whilst  others 
again  have  teeth  rigidly  fixed.  So  that  within  the  limits  of 
a  single  family  we  have  several  steps  in  a  gradual  progres¬ 
sion  towards  a  very  highly  specialised  organ. 

In  the  hinged  teeth  already  alluded  to  the  purpose  served 
by  their  mobility  seems  to  be  the  catching  of  active  fish,  and 
the  elasticity  resides  solely  in  the  hinges;  but  the  common 
Pike  possesses  many  hinged  teeth  which  seem  to  be  concerned 
in  the  swallowing  of  the  prey  after  it  has  been  caught,  and 
there  is  no  elasticity  in  the  hinges,  the  resilience  of  the  teeth 
being  provided  for  in  another  way. 

The  teeth  which  surround  the  margins  of  the  jaws  are 
anchylosed,  and  they  are  more  or  less  solidly  filled  up  in 
their  interior  with  a  development  of  osteodentine,  which,  by 
becoming  continuous  with  the  subjacent  bone,  cements  them 
upon  it.  The  manner  of  development  of  this  is  by  rods  of 
calcifying  material  shooting  down  through  the  central  pulp 
(see  page  175);  in  the  hinged  teeth  also  these  trabeculae  shoot 

i  %  i  ■  \  ■  ■  j  J  «  .  e  c  a 


THE  ATTACHMENT  OF  TEETH. 


217 


down,  and  become  continuous  with  the  subjacent  bone,  only 
instead  of  rigidly  ossifying  they  remain  soft  and  elastic,  so 

Fig.  90  ('). 


that  the  tooth  is  like  an  extinguisher  fastened  down  by  a 
large  number  of  elastic  strings  attached  to  different  points 
on  its  interior,  and  hinged  at  one  side. 

The  elasticity  is  very  perfect,  so  that  the  teeth  depressed 
and  suddenly  released  return  with  an  audible  snap,  but  it 

f1)  Hinged  tooth  of  Pike.  a.  Dentine,  b.  Elastic  rods,  formed  of 
uncalcified  trabeculae  which  might  have  become  bone.  c.  Hinge,  not  itself 
elastic,  d.  Bone  of  attachment,  e.  Bone  of  body  of  jaw. 


218 


A  MANUAL  OF  DENTAL  ANATOMY. 


have  been  described  by  Dr.  Gunther,  through  whose  kindness 
I  have  had  the  opportunity  of  examining  them,  are  several 
which  possess  hinged  teeth.  Thus  in Bathysaurus  ferox,  which 

(*)  Hinged  tootli  of  Odontostomus.  a.  Enamel  penetrated  by  dentinal 
tubes,  b .  Dentine, 


resides  solely  in  these  strings,  for  if  these  be  divided  by 
carefully  slipping  a  cataract  needle  under  the  tooth  without 
injuring  the  hinge,  the  tooth  will  stay  in  any  position  into 
which  it  is  put. 

Amongst  the  very  peculiar  predatory  fish  which  were 
obtained  by  the  Challenger  from  great  depths,  and  which 

Fig.  91  (!) 


FioM. 

O 


THE  ATTACHMENT  OF  TEETH. 


219 


has  a  crocodile-like  snout,  the  teeth  are  of  no  very  great  size, 
but  they  are  attached  by  ligamentous  hinges  which  allow  of 
their  being  bent  down  backwards  and  inwards.  The  teeth 
are  not  perched  upon  any  definite  pedestals,  so  that  the 
motion  is  not  very  exactly  limited  to  one  plane.  But  in  Odon- 
tostomus  hyalinus  there  are  some  more  highly  specialised 
hinged  teeth,  which  are  laterally  compressed,  and  have  a  sort 
of  barbed  point  which  recalls  the  form  of  some  primitive  bone 
fish-hooks.  The  vomer  carries  two  such  teeth  of  great  length, 
behind  which  come  some  smaller  ones :  they  are  perched 
upon  little  bony  pedestals  of  such  form  that  the  attachment 
being  made  by  means  of  an  elastic  ligament  on  one  side,  the 
motion  permitted  to  the  tooth  is  strictly  confined  to  one  plane. 

Thus  we  have  examples  of  hinged  teeth  occurring  in  several 
distinct  orders  of  fish ;  in  Acanthopterygii  (Lophius),  in 
Anacanthina  (Merlucius),  in  Physostomi  (Esox,  Bathysaurus, 
Odontostomus),  whilst  on  the  other  hand  they  are  not 
universal  even  within  the  limits  of  well-defined  families. 

The  points  most  noteworthy  are,  (i.)  that  hinged  teeth 
have  arisen  independently  in  families  of  fish  widely  removed 
from  one  another,  and  (ii.)  that,  whilst  the  general  object  of 
mobility  and  elastic  resiliency  is  attained  in  all,  it  is  by  a 
different  mechanism,  and  by  the  least  possible  modification 
of  the  existing  fixed  teeth  of  the  family. 

Attachment  by  Anchylosis. — In  both  the  socketed  and 
the  membranous  manners  of  attachment  an  organised,  more 
or  less  vascular  membrane,  intervenes  between  the  tooth  and 
the  jaw-bone  ;  in  the  method  now  under  consideration  there 
is  no  such  intervening  membrane,  but  the  calcified  tooth  sub¬ 
stance  and  the  bone  are  in  actual  continuity,  so  that  it  is  often 
difficult  to  discern  with  the  naked  eye  the  line  of  junction. 

The  teeth  may  be  only  slightly  held,  so  that  they  break  off 
under  the  application  of  only  a  moderate  degree  of  force,  or 
!  they  may  be  so  intimately  bound  to  the  bone  that  a  portion 
of  the  latter  will  usually  be  torn  away  with  the  tooth. 


220 


A  MANUAL  OF  DENTAL  ANATOMY. 


.  A  very  perfect  example  of  attachment  by  anchylosis  is 
afforded  by  the  fixed  teeth  of  the  Pike,  of  which  the  central 
cone  is  composed  of  osteodentine.  The  method  by  which  the 
entire  fusion  of  this  tissue  with  the  bone  beneath  it  takes 
place  has  already  been  alluded  to,  the  similarity  of  its 
method  of  calcification  with  that  of  bone  rendering  the  fusion 
easy  and  complete. 

And  in  certain  extinct  fish,  whose  nearest  ally  is  the  now 
anomalous  Australian  shark,  the  Cestracion  philippi,  the  lower 
part  of  the  tooth  is  composed  of  osteodentine,  which  so  closely 
resembles  bone  itself  that  it  is  impossible  to  say  at  which 
point  the  bone  may  be  said  to  commence  and  the  tooth  to 
end ;  but  even  where  this  intimate  resemblance  in  histological 
character  does  not  exist,  there  is  often  to  be  found  more  or 
less  blending  of  the  basal  dentine  with  the  bone  beneath  it, 
so  that  there  is  even  here  a  sort  of  transitional  region. 

From  the  accounts  which  pass  current  in  most  text  books 
it  would  be  supposed  that  the  process  of  attachment  by 
anchylosis  is  a  very  simple  matter,  the  base  of  the  dentine 
papilla,  or  the  dental  capsule,  by  its  calcification  cementing 
the  tooth  on  to  a  surface  of  the  jaw-bone  already  formed. 
In  a  few  animals  which  I  have  examined  (*),  however,  I 
have  found  that  this  conception  docs  not  at  all  adequately 
represent  what  really  takes  place  ;  it  seldom,  perhaps  never, 
happens  that  a  tooth  is  attached  directly  to  a  plane  surface 
of  the  jaw  which  has  been  formed  previously;  but  the  union 
takes  place  through  the  medium  of  a  portion  of  bone  (which 
may  be  large  or  small  in  amount)  which  is  specially  developed 
to  give  attachment  to  that  one  particular  tooth,  and  after 
the  fall  of  that  tooth  is  itself  removed. 

For  this  bone  I  have  proposed  the  name  of  “bone  of 
attachment,”  and  it  is  strictly  analogous  to  the  sockets  of 
those  teeth  which  have  sockets.  It  is  well  exemplified  in 

4 

f1)  Transactions  of  the  Odontological  Society,  Dec.  1874. — “Studies  on 
the  Attachment  of  Teethe”  •  •  -  - 


THE  ATTACHMENT  OF  TEETH. 


221: 


the  Ophidia,  a  description  of  the  fixation  of  the  teeth  of 
which  will  serve  to  convey  a  good  idea  of  its  general  cha¬ 
racter.  If  the  base  of  one  of  the  teeth,  with  the  subjacent 
jaw-bone,  be  submitted  to  microscopic  examination  we  shall 
find  that  the  layer  of  bone  which  closely  embraces  the  tooth 
contrasts  markedly  with  the  rest  of  the  bone.  The  latter  is 
fine  in  texture  its  lacunae,  with  their  very  numerous  fine 


canaliculi,  very  regular,  and  the  lamination  obviously  refer¬ 
able  to  the  general  surface  of  the  bone.  But  the  “  bone 
of  attachment”  is  very  coarse  in  texture,  full  of  irregular 
spaces,  very  different  from  the  regular  lacunae,  and  its  lamin¬ 
ation  is  roughly  parallel  with  the  base  of  the  tooth.  The 
dentine  of  the  base  of  the  tooth  also  bends  inwards  (Fig.  92), 
and  its  tubes  are  lost  in  the  osseous  tissue,  a  blending  so 
intimate  resulting,  that  in  grinding  down  sections  the  tooth 
and  the  bone  of  attachment  often  come  away  together,  the 

p)  Section  of  tooth  and  a  portion  of  the  jaw  of  a  Python,  showing  the 
!  marked  difference  in  character  between  the  bone  of  attachment  and  the 
rest  of  the  bone. 


222 


A  MANUAL  OF  DENTAL  ANATOMY. 


tooth  and  this  bone  being  more  intimately  united  than  this 
special  bone  is  with  that  of  the  rest  of  the  jaw. 

A  study  of  its  development  also  proves  that  it  has  an  in¬ 
timate  relation  with  the  tooth  with  which  it  is  continuous, 
for  it  is  wholly  removed  with  the  fall  of  the  tooth,  and  is 
specially  developed  again  for  the  next  tooth  which  comes 
into  position.  The  periosteum  of  the  rest  of  the  jaw-bone 
appears  to  take  an  important  share  in  the  formation  of  this 
special  bone  substance,  and  the  tooth  capsule,  by  its  ossifi¬ 
cation,  apparently  contributes  little. 

In  the  frog  the  teeth  are  commonly  described  as  being 
attached  by  their  bases  and  outer  surface  to  a  continuous 
groove,  of  which  the  external  wall  is  the  highest.  Such  is, 
however,  an  inadequate  description  of  the  process,  the  tooth 
as  seen  in  section,  being  attached  on  its  outer  side  by  a  new 
development  of  special  bone,  which  extends  for  a  short 
distance  up  over  its  external  surface  ;  and  for  the  support  of 
its  inner  wall  there  springs  up  from  the  subjacent  bone  a 
pillar  of  bone,  which  is  entirely  removed  when  that  tooth 
falls,  a  new  pillar  being  developed  for  the  next  tooth. 

When  the  teeth  are,  as  in  many  fish,  implanted  upon 
what  to  the  naked  eye  appears  nothing  more  than  a  plane 
surface  of  bone,  a  microscopic  examination  generally,  in  fact 
in  all  specimens  which  I  have  examined,  reveals  that  the 
individual  teeth  are  implanted  in  depressions  much  larger 
than  themselves,  the  excess  of  space  being  occupied  by  new 
and  specially  formed  bone,  or  else  that  the  teeth  surmount 
pedicles,  which  are  closely  set  together,  the  interspaces  being 
occupied  with  a  less  regular  calcified  structure. 

A  good  example  of  the  latter  method  is  afforded  by  the  Eel 
(Fig.  93),  in  which  each  tooth  surmounts  a  short  hollow  cylin¬ 
der  of  bone,  the  lamination,  Ac.,  of  which  differs  strongly 
irom  that  of  the  body  of  the  j  aw-bone.  When  the  tooth  which 
it  carries  is  shed,  the  bone  of  attachment,  in  this  case  a  hollow 
cylinder,  is  removed  right  down  to  the  level  of  the  main 
bone  of  the  jaw,  as  is  well  seen  in  the  figure  to  the  left  of 


THE  ATTACHMENT  OF  TEETH 


223 


the  teeth  in  position.  Under  a  higher  magnifying  power 
the  bone  at  this  point  would  be  found  to  be  excavated  by 
“  Howship’s  lacunae.”  As  an  anchylosis,  the  implantation 
of  the  teeth  is  less  perfect  than  that  of  those  of  the  snake, 
for  the  dentinal  tubes  at  the  base  of  the  tooth  are  not  de¬ 
flected,  and  do  not  in  any  sense  blend  with  the  bone  beneath 
them.  Accordingly,  the  teeth  are  far  less  firmly  attached, 
and  break  off  quite  readily. 

i 

Fig.  93  (*). 


A  transition  towards  the  socketed  type  of  implantation  is 
furnished  by  some  of  the  cod  family.  In  the  haddock,  for 
example,  the  teeth  surmount  hollow  cylinders  of  “  bone  of 
attachment,”  resembling  in  many  particulars  those  of  the 
eel ;  the  teeth  do  not,  however,  simply  surmount  the  bony 
cylinders,  but  are  continued  for  a  short  distance  within  them, 
definite  shoulders  being  formed  which  rest  on  the  rims  of  the 
cylinder.  The  base  of  the  tooth  does  not,  however,  contract 
or  taper  any  more,  and  is  widely  open,  so  that  it  cannot  be 
considered  that  any  close  approximation  to  a  root  is  made. 

fl)  From  lower  jaw  of  an  Eel.  a.  Bone  of  jaw.  b.  Bone  of  attach¬ 
ment.  d.  Dentine,  f.  Enamel,  g.  Space  vacated  by  a  shed  tooth. 


224 


A  MANUAL  OF  DENTAL  ANATOMY. 


The  pulp  cavity  of  the  tooth  becomes  continuous  with  the 
cavity  of  the  osseous  cylinder,  into  which  it  is  for  a  short 
distance  continued. 

The  bony  supports  of  the  teeth  originate  in  many  osseous 
trabecula)  which  spring  up  simultaneously  from  the  bone  of 
the  jaw  beneath  the  new  tooth  ;  these  coalesce  to  form  a 
net-like  skeleton,  which  rapidly  becomes  filled  in  by  the 
progress  of  ossification.  So  far  as  my  own  researches  enable 
me  to  say,  there  is  this  much  in  common  in  all  forms  of 


Fig.  94  f1). 


attachment  by  anchylosis,  no  matter  how  different  the 
naked  eye  results  of  the  process  may  be  ;  the  tooth,  as  it 
comes  into  position,  is  secured  by  an  exceedingly  rapid 
development  of  bone,  which  is  more  or  less  directly  an 
outgrowth  from  the  jaw-bone  itself,  which  is  in  some  un¬ 
seen  manner  stimulated  into  activity  by  the  proximity  of  the 
tooth.  In  amount  this  specially  formed  bone  varies  greatly, 
but  in  all  instances  it  is  not  the  tooth  capsule,  but  tissues 
altogether  external  to  this,  which  serve  to  secure  the  tooth 
in  its  place  by  their  ossification. 

(b  From  lower  jaw  of  a  Haddock,  a.  Bone  of  jaw.  b.  Bone  of  attach¬ 
ment.  d.  Dentine  of  tooth. 


THE  ATTACHMENT  OF  TEETH. 


225 


The  teeth  of  the  mackerel  present  an  interesting  variety  of 
attachment  by  anchylosis.  The  margins  of  the  jaws  are  very 
thin,  and  by  no  means  fleshy,  and  in  this  thin  margin  there 
is  a  deep  groove  between  the  outer  and  inner  plate  of  the 
bone.  In  this  groove  are  the  teeth,  their  sharp  points  pro¬ 
jecting  beyond  the  edges  of  the  bone,  and  they  are  held  in 
their  place  by  a  network'  or  scaffolding  of  bone  of  attach¬ 
ment  which  is  developed  between  their  sides  and  the  inner 


Fig.  95  (J). 


surface  of  the  bone.  They  are,  so  to  speak, |  hung  up  in 
their  place,  and  their  open  bases  rest  on  nothing,  or  at  least 
on  nothing  hard. 

Attachment  by  implantation  in  a  socket. — In  this, 
as  in  anchylosis,  there  is  a  special  development  of  bone, 
which  is  modelled  to  the  base  of  the  tooth,  but  instead  of 
ts  being  in  actual  close  continuity  with  the  dental  tissues, 
here  intervenes  a  vascular  organised  membrane.  The 
nanner  in  which  the  sockets  are,  so  to  speak,  plastered 

fl)  Tooth  of  Mackerel,  showing  its  peculiar  mode  of  anchylosis. 
I.  Tooth,  b.  Bone  of  jaw.  c.  gums  and  stems,  d.  Bone  of  attachment. 


Q 


226 


A  MANUAL  OF  DENTAL  ANATOMY. 


around  the  roots  of  the  teeth,  and  are  perfectly  subservient 
to  and  dependent  on  them,  has  already  been  described  ;  little, 
therefore,  need  be  added  here,  save  that  the  soft  tissue 
intervening  between  the  bone  and  the  tooth  is  not  sepa¬ 
rable,  either  anatomically  or  from  the  point  of  view  of 
development,  into  any  two  layers,  but  is  a  single  mem¬ 
brane,  termed  the  “  alveolo-dental  periosteum.”  That  it  is 
single,  is  a  matter  of  absolute  certainty;  there  is  no  difficulty 
in  demonstrating  it  in  situ,  with  vessels  and  bundles  of 
fibres  traversing  its  whole  thickness  from  the  tooth  to  the 
bone,  or  vice  versd. 

The  nature  and  development  of  the  sockets  in  those 
few  reptiles  and  fishes  which  have  socketed  teeth  require 
further  examination.  I  am  not,  from  what  I  have  seen  in 
sections  of  the  jaws  of  a  young  crocodile,  inclined  to  regard 
them  as  in  all  respects  similar  to  the  alveoli  of  mammalian 
teeth.  At  all  events  they  are  not  developed  in  that  same 
subserviency  to  each  individual  tooth ;  on  the  contrary, 
successive  teeth  come  up  and  occupy  a  socket  which  is 
more  or  less  already  in  existence. 

Although  there  are  animals  in  which  implantation  in  a 
spurious  socket  is  supplemented  by  anchylosis  to  the  wall 
or  to  the  bottom  of  the  socket,  no  example  of  anchylosis 
occurring  between  the  tooth  and  the  bone  of  the  socket  has 
ever  been  met  with  in  man,  or  indeed  in  any  mammal 
exemplifying  a  typical  socketed  implantation  of  the  teeth. 


Hunter.  On  the  Anatomy  of  the  Human  Teeth. 

Tomes.  J.  Dental  Surgery.  1869. 

Hcjmphery.  Transact.  Camb.  Philos.  Soc.  1863. 

Wedl.  Pathology  of  the  Teeth. 

Heudner.  Beitrage  zur  Lehre  von  der  Knochenentwickelung,  &c. 
Tomes,  Charles  S.  On  Vascular  Dentine  and  Hinged  Teeth. 

Philos.  Transac.,  1878,  and  Quart.  Journal 
Micros.  Science,  vol.  xvii.  new  series. 
Transac.  Odontolog.  Soc.  1874 — 1876. 


CHAPTER  VI. 


THE  TEETH  OF  FISHES. 

In  the  following  pages  nothing  more  than  a  brief  account 
of  a  few  typical  forms  can  be  attempted  ;  the  limits  of  space 
forbid  the  mention  of  many  creatures,  or  the  insertion  of 
detailed  descriptions  of  the  dentition  even  of  the  few  which 
are  included.  In  the  'class  of  fish  the  task  of  selec¬ 
tion  of  the  forms  for  description  is  no  easy  one ;  for 
the  almost  infinite  diversity  of  dentition  which  exists  in 
it  makes  it  a  matter  of  peculiar  difficulty  to  frame  any 
general  account,  or  to  do  more  than  present  before  the 
reader  a  description  of  a  few  individual  forms  from  which 
he  may  gather,  as  best  he  can,  a  general  idea  of  piscine 
dentition. 

The  class  of  Fishes  is  divided  into  four  sub-classes  : — 

Leptocardii.  Heart  replaced  by  pulsating-  sinuses.  Skeleton  noto¬ 
chordal  and  membrano-cartilaginous.  No  skull,  no  brain. 
Cyclostomata.  Head  without  bulbus  arteriosus.  Skeleton  car¬ 
tilaginous  and  notochordal.  No  jaws  ;  mouth  surrounded  by  a 
circular  lip. 

Teleostei.  Non-contractile  bulbus  arteriosus.  No  spiral  valve 
in  intestine.  Optic  nerves  decussating.  Skeleton  ossified,  with 
completely  separated  vertebrae. 

Palahichthyes.  Heart  with  contractile  conus  arteriosus  ;  intestine 
with  spiral  valve  ;  optic  nerve  non-decussating  or  only  partially 
decussating. 

Of  Leptocardii  (the  single  genus  Amphioxus  or  Branchio- 
stoma),  there  is  nothing  to  be  said,  as  it  has  no  jaws  and 
jtherefore  no  teeth. 

The  Cyclostomata  comprise  the  lampreys  and  the  very 
peculiar  parasitic  fishes,  the  Myxine  and  Bdellostoma,  which 


228 


A  MANUAL  OF  DENTAL  ANATOMY. 


bore  their  way  into  the  bodies  of  other  fish  ;  the  cod  is  often 
attacked  by  the  Myxine.  The  lampreys,  which  also  are  pre¬ 
datory,  attaching  themselves  by  their  sucking  mouth  to  the 
bodies  of  other  fish  from  which  they  scrape  off  the  flesh, 
have  a  round  mouth,  the  margins  of  which  are  beset  with 
rows  of  small  conical  teeth,  there  being  two  larger  blade¬ 
shaped  teeth,  called  from  their  relative  position  the  man¬ 
dibular  and  maxillary  teeth  in  the  centre. 

Until  recently  little  was  known  of  the  structure  of  horny 
teeth,  but  they  have  been  investigated  by  Dr.  Beard  (Cen- 
tralblatt  f.  Wissen.  Anat.  iii.  1888,  nr.  6),  who  finds  that  the 
horny  cone  rests  upon  a  slight  dermal  papilla,  and  fits  into 
special  epidermal  depressions  at  the  base  of  the  papilla  (in 
Pteromyzon  fluviatilis) ;  but  in  P.  marinus  there  are  three 
superimposed  cones,  “like  a  nest  of  Chinese  boxes.”  Each 
of  these  layers  arises  from  a  separate  epidermal  depression, 
which  goes  on  continually  forming  horn,  so  that  the  under 
cones  are  in  no  sense  reserve  teeth,  for  as  each  tooth  is  worn 
away  at  the  apex  fresh  horny  matter  is  formed  below  and 
pushed  forwards.  There  is  thus  no  resemblance  to  the  teeth 
of  higher  vertebrates. 

In  a  young  lamprey  there  are  to  be  found  what  at  first 
sight  look  like  true  tooth  sacs,  but  the  dental  papilla  never 
forms  any  odontoblasts,  and  the  epithelium  which  corres¬ 
ponds  to  the  enamel  organ  produces  horn ;  this  is  true  of 
the  marginal  teeth,  but  further  in  towards  the  centre  the 
teeth  are  formed  simply  in  the  basal  layers  of  the  epithelium, 
without  the  intervention  of  any  sort  of  tooth  sac. 

But  in  the  Myxine  and  Bdellostoma  there  is  a  very  in¬ 
teresting  and  unexpected  arrangement  of  structures.  They 
have  a  large  sharply  pointed  median  tooth  and  two  comb¬ 
like  smaller  teeth  upon  the  tongue,  and  the  working  surface 
of  the  teeth  is  composed  of  horn  similar  both  in  structure  and 
development  to  that  found  in  the  lamprey. 

Dr.  Beard  describes  the  tooth  of  Bdellostoma  as  consisting 


THE  TEETH  OF  FISHES. 


229 


of  a  cap  of  horn  which  is  thick  and  strong  and  of  a  bright 
yellow  colour ;  beneath  this  comes  a  layer  of  epithelium, 
and  next  to  this  a  hard  calcified  material,  which  is  to  be 
regarded  as  some  form  of  dentine. 

The  horny  cap  is  fitted  into  an  epithelial  groove  at  its 
base,  so  that  it  increases  in  length  from  the  cells  of  this 
groove  becoming  cornified,  and  in  thickness  by  a  similar 
conversion  of  the  epithelial  layer  beneath  it. 

The  hard  cone  which  forms,  so  to  speak,  the  body  of  the 
tooth  is  an  anomalous  structure  not  closely  corresponding 
with  any  known  form  of  dentine,  but  yet  it  is  undoubtedly 
the  product  of  an  odontoblast  layer  upon  the  pulp,  which 
latter  remains  in  the  base  of  the  cone  of  dentine  in  the  usual 
way. 

The  great  hardness  of  the  tooth  and  of  the  horny  cap 
renders  it  a  very  difficult  matter  to  get  good  sections,  and 
hence  the  minute  structure  has  not  been  very  fully  de¬ 
scribed.  At  the  apex  of  the  cone  is  a  thin  structureless 
layer,  which  Dr.  Beard  thinks  may  be  enamel  (the 
frequent  occurrence  of  thin  outer  structureless  layers  upon 
dentine  however  would  seem  to  render  this  determination 
open  to  uncertainty).  There  is,  however,  a  layer  of  epithe¬ 
lium,  in  the  proper  situation,  which  has  the  characters  of  an 
enamel  organ  in  so  far  as  the  presence  of  long  columnar 
cells  go. 

The  dentine  cap  appears  to  contain  small  dentinal  tubes, 
and  also  vascular  canals  of  larger  size  arranged  with  consider¬ 
able  regularity. 

It  is  difficult  to  conceive  that  the  presence  of  the  calcified 
cone  can  be  of  much,  if  any,  service  whilst  buried  beneath  the 
horny  cap,  and  we  must  regard  these  horny  teeth  not  as  an 
earlier  and  simple  form  of  tooth,  but  as  being  degenerated 
teeth.  And  they  would  thus  lend  support  to  the  idea  already 
arrived  at  on  other  grounds  that  these  fish  had  as  ancestors 
fish  which  had  jaws  and  teeth  carried  upon  them. 


230 


A  MANUAL  OF  DENTAL  ANATOMY. 


It  is  to  be  noted  that  the  relation  which  the  horn  cone 
bears  to  the  dental  papilla  and  to  its  dentine  is  entirely 
different  from  that  borne  by  the  horny  teeth  of  Ornitho¬ 
rhyncus,  in  which  the  horny  plate  wdiich  takes  the  place  of 
teeth  in  the  adult  lies  beneath  the  teeth. 

It  has  been  suggested  by  Dr.  Beard  that  the  fusion  of  the 

Fig.  96  f1). 


he 


P 

lingual  teeth  of  Myxine  into  a  serrated  plate  may  indicate  the 
manner  in  which  the  serrated  horny  jaws  of  Chelonians  may 
have  originated,  as  a  substitution  of  horny  tissue  for  true  teeth 
upon  which  they  were  once  superimposed ;  and  similar 
speculations  have  been  indulged  in  as  to  the  manner  in 
which  the  bird’s  bill  may  have  originated  from  the  substitu¬ 
tion  of  a  number  of  coalescent  horny  teeth  for  true  teeth, 
but  the  material  for  such  generalisation  is  not  yet  to  hand. 

As  in  the  matter  of  teeth  the  Palteichthyes,  comprising  the 
Sharks  and  Rays  and  the  Ganoid  fish,  present  somewhat  simpler 

f1)  Tooth  of  Bdellostoma,  Semidiagrammatic,  after  Dr.  Beard,  d.  Cal¬ 
cified  dentine  cap.  e.  (?)  Enamel.  h.  Horny  tooth.  he.  Epithelial 
groove  in  which  the  bone  is  formed,  p.  Pulp. 


THE  TEETH  OF  FISHES. 


231 


conditions  that  are  met  with  in  the  osseous  fish,  it  will  be 
convenient  to  describe  their  teeth  first,  although  in  most 
respects  they  stand  at  the  head  of  the  class  of  fishes,  and 
present  many  indications  of  affinity  with  the  Batrachia. 

In  Sharks  the  scales  are  replaced  by  calcified  papilla),  which 
have  the  structure  of  the  teeth:  to  these  the  “ shagreen, ” 
as  shark  skin  is  termed,  owes  its  roughness ;  the  mouth 
is  a  transverse,  more  or  less  curved  fissure,  opening 
upon  the  under  surface  of  the  head  at  some  little  distance 
behind  the  end  of  the  snout.  Hence  it  is  that  a  shark  in 

j 

seizing  its  prey  turns  over  upon  its  back  or  at  all  events 
upon  its  side. 

The  jaws,  which  are  made  up  of  the  representatives  of  the 
palato-quadrate  arch,  and  of  Meckel’s  cartilage,  neither  true 
maxillae  nor  premaxillae  being  present,  are  cartilaginous  in 
the  main  (although  covered  with  a  more  or  less  ossified  crust), 
and  therefore  shrink  and  become  much  distorted  in  drying. 
The  shape  of  the  jaws  differs  in  the  various  groups  of 
Plagiostomi,  in  some  each  of  the  two  jaws  being  a  tolerably 
perfect  semicircle,  while  in  others  they  are  nearly  straight 
and  parallel  to  one  another  (see  Fig.  97  and  Fig.  101);  but 
in  all  the  rounded  working  surface  of  the  jaw  is  clothed 
or  encased  by  teeth,  which  are  arranged  in  many  parallel 
concentric  rows. 

The  teeth,  which  are  situated  upon  the  edge  or  exposed 
border  of  the  jaw,  are  usually  erect,  whilst  the  rows  which 
lie  behind  them,  farther  within  the  mouth,  point  backwards, 
and  are  more  or  less  recumbent,  not  having  yet  come  into 
full  use. 

In  this  respect,  however,  marked  difference  exists  among 
various  genera  of  sharks ;  for  instance  in  the  great  tropical 
white  shark  the  teeth  which  lie  on  the  border  of  the  jaw 
are  erect,  and  all  the  successive  rows  are  quite  recumbent, 
whereas  in  many  of  the  dog-fishes  the  inner  surface  of  the 
jaws  forms  an  even  rounded  surface  along  which  the  rows  of 


232 


A  MANUAL  OF  DENTAL  ANATOMY. 


teeth  are  disposed  in  every  intermediate  position  between 
those  fully  recumbent  at  the  innermost  part  of  the  jaw, 
and  those  fully  erected  upon  its  exposed  borders.  Only  a 
few  of  the  most  forward  rows  of  teeth  are  exposed,  a  fold 
or  flap  of  mucous  membrane  covering  in  those  teeth  which 


T-l  M  /  1  \ 


are  not  as  yet  fully  calcified  and  firmly  attached  to  the 


gums. 

In  Lamna,  which  may  be  taken  as 


fairly  illustrative,  the 


teeth  are  arranged  round  the  jaws  in  concentric  rows  with 
great  regularity,  the  teeth  of  the  successive  rows  correspond¬ 
ing  in  position  to  the  teeth  of  older  rows,  and  not,  as  is  the 
case  in  some  other  sharks,  to  their  interspaces.  They  are 
attached  by  being  embedded  in  a  densely  fibrous  gum,  which 
closely  embraces  their  bifurcated  bases  ;  and  this  dense  gum, 
carrying  with  it  the  teeth,  slides  bodily  upwards  over  the 
inner  face  of  the  jaw,  and  outwards  over  its  border,  beyond 
which  it,  to  borrow  a  phrase  from  geological  science,  has  an 
“  outcrop.” 

P)  Lower  jaw  of  Lamna.  a.  Edge  of  flap  of  mucous  membrane  which 
covers  in  the  teeth  not  yet  completed. 


THE  TEETH  OF  FISHES. 


233 


In  Lamna  the  second  and  third  rows  of  teeth  are  only 
partially  erect,  the  rows  behind  these  lying  recumbent,  and 
being  in  the  fresh  state  covered  in  by  the  fold  of  mucous 
membrane,  which,  being  dried  and  shrunk  in  the  specimen 
figured,  falls  short  of  its  original  level. 

Fig.  98  (*). 


Thus  rows  of  teeth  originally  developed  at  the  base  of 
the  jaw  are  carried  upwards,  come  to  occupy  the  foremost 
position  on  the  border  of  the  jaw,  and  are  cast  off  when 
they  pass  the  point  /in  the  figure.  It  is  thus  easy  to  under¬ 
stand  why  sharks’  teeth  are  so  abundantly  found  in  a  fossil 
condition,  although  other  indications  of  the  existence  of  the 

(b  Transverse  section  of  lower  jaw  of  a  Dog-fish.  a.  Oral  epithelium, 

|  b.  Oral  epithelium  passing  on  to  flap.  c.  Protecting  flap  of  mucous  mem- 
■  brane  (thecal  fold).  d.  Youngest  dentine  pulp.  e.  Youngest  enamel 
organ.  /.  Tooth  about  to  be  shed.  g.  Calcified  crust  of  jaw. 


234 


A  MANUAL  OF  DENTAL  ANATOMY. 


fish  are  rare  enough  ;  for  every  shark  in  the  course  of  its 
life  casts  off  great  numbers  of  teeth,  which  fall  to  the 
bottom  of  the  sea  and  become  bedded  in  the  deposit  there 
forming. 

The  teeth  are  never  anchylosed  to  the  jaw,  nor  have  they 
any  direct  connection  with  it,  but,  as  before  mentioned,  are 
retained  by  being  bedded  in  a  very  tough  fibrous  membrane  ; 
the  nature  of  their  fixation  has  been  more  exactly  described 
at  another  page  (page  213). 

The  sheet  of  fibrous  gum  slides  bodily  over  the  curved 
surface  of  the  jaw,  continually  bringing  up  from  below 
fresh  rows  of  teeth,  as  was  proved  by  Andre’s  specimen, 
and  it  may  be  worth  while  to  condense  from  Professor 
Owen  the  description  of  the  manner  in  which  it  was  thus 
proved  that  an  actual  sliding  or  rotation  of  the  membrane 
does  really  take  place,  and  that  the  whole  bony  jaw  itself 
does  not  become  slowly  everted.  The  spine  of  a  sting  ray 
had  been  driven  through  the  lower  jaw  of  a  shark  (Galeus), 
passing  between  two  (vertical)  rows  of  teeth  which  had 
not  yet  been  brought  into  use  ;  when  the  specimen  came 
under  observation  the  spine  had  remained  in  this  situation, 
transfixing  the  jaw,  for  a  long  time,  as  was  evidenced  by  all 
the  teeth  of  these  two  rows,  both  above  and  below  it,  being 
stunted  and  smaller  than  their  neighbours. 

Hence  the  development  of  these  teeth,  which  ultimately 
came  to  be  at  some  little  distance  from  the  spine,  had  been 
profoundly  modified  by  its  presence,  and  it  is  difficult  to 
understand  in  Avhat  manner  this  could  have  affected  them 
had  they  not,  at  an  earlier  period  of  their  growth,  lain  in 
more  immediate  proximity  to  it.  But  if  the  membrane, 
with  the  teetli  attached,  does  move  slowly  along  the  surface 
of  the  jaw,  this  difficulty  at  once  disappears. 

The  forms  of  the  teeth  in  various  sharks  are  different 
and  characteristic ;  nevertheless  they  vary  somewhat  with 
age  in  some  species,  and  present  differences  in  size  and 


THE  TEETH  OF  FISHES. 


235 


form  in  the  upper  and  lower  jaws,  or  in  different  parts  of 
the  mouth  of  the  same  individual.  For  instance,  in  Lamna, 
in  the  upper  jaw,  the  third  teeth  of  each  horizontal  row, 
counting  from  the  middle  line,  are  very  small,  while  in  both 
jaws  there  is  a  gradual  diminution  in  the  size  of  the  teeth 
towards  the  back  of  the  mouth. 

Thus,  although  it  is  often  possible  to  refer  a  particular 
tooth  to  its  right  genus  or  even  species,  much  care  is  re¬ 
quisite  in  so  doing. 

The  teeth  of  the  bloodthirsty  white  shark  (Carcharias) 
are  triangular  flattened  plates,  rounded  on  their  posterior 
aspect,  with  trenchant  slightly  serrated  edges ;  it  is  pointed 
out  by  Professor  Owen  that  if  the  relation  between  the  size 
j  of  the  teeth  and  that  of  the  body  were  the  same  in  extinct 
as  in  recent  sharks,  the  dimensions  of  the  teeth  of  the 
tertiary  Carcharodon  would  indicate  the  existence  of  sharks 
as  large  as  whales. 

The  intimate  relationship  between  the  teeth  and  the 
dermal  spines,  which  from  the  standpoint  of  development, 
has  been  illustrated  at  page  2  and  page  123,  is  apparent 
also  in  their  histological  structure.  There  are  many  dermal 
spines  to  be  met  with  in  the  sharks,  which  seen  alone  could 
not  possibly  be  distinguished  from  teeth,  the  resemblance 
both  in  outer  form,  in  minute  structure,  and  manner  of 
development  being  most  complete.  The  tooth  figured  on 
page  49  is  a  fair  example  of  a  structure  very  common  among 
the  sharks,  viz.,  a  central  body  of  osteodentine,  the  outer 
portion  of  which  has  dentinal  tubes  so  fine,  regular,  and 
closely  packed  as  to  merit  the  name  of  hard  unvascular 
dentine,  and  over  this  again  a  thin  varnish  of  enamel.  (?) 

And  yet  no  observer  from  its  structure  alone  could  feel 
sure  whether  it  was  a  large  dermal  spine,  or  a  tooth.  Dental 
tissues  occur  in  other  parts  of  the  mouths  of  Selachia  than 
upon  the  jaws,  not  only  in  the  embryonic  stages,  but  in  the 
adult.  Thus  Professor  Sir  W.  Turner  has  described  (Proc. 


236 


A  MANUAL  OF  DENTAL  ANATOMY. 


Roy.  Society,  Edinburgh,  1880),  very  numerous  comb-like 
appendages  5  inches  long  upon  the  branchial  arches  of  the 
Basking  Shark  (Selache  maxima),  which  apparently  perform 
the  same  function  as  whalebone  in  straining  the  water. 
These  combs  are  formed  of  a  variety  of  dentine  (?  osteo- 
dentine),  and  closely  resemble  in  structure  the  true  teeth, 
which  are  however  very,  small  in  this  shark. 

In  the  seas  of  Australia  there  exists  a  Shark,  the 
Oestracion  Philippi,  with  a  very  aberrant  dentition,  to  which 
great  interest  attaches,  inasmuch  as  it  is  the  sole  surviving 
representative  of  forms  once  spread  all  over  the  world.  In 
the  front  of  the  mouth  the  teeth  are  small  and  very 
numerous  ;  they  are  flat  plates  fitted  by  their  edges  to 
one  another,  while  from  their  centres  spring  up  sharp  points, 
soon  worn  off  when  the  tooth  reaches  such  a  position  upon 
the  jaw  that  it  comes  into  use. 

Proceeding  backwards,  the  teeth  cease  to  be  pointed, 
increase  in  size,  and  become  fewer  in  each  row ;  a  reference 
to  the  figure  will  convey  a  better  idea  of  their  general  form 
than  any  description.  Those  which  have  come  into  use 
are,  towards  the  back  of  the  mouth,  always  much  worn ; 
their  shedding  and  renewal  takes  place,  as  in  other  sharks, 
by  a  rotation  of  the  mucous  membrane  over  the  surface  of 
the  jaw,  so  that,  as  might  have  been  expected,  large 
numbers  of  the  isolated  fossil  teeth  of  Cestracionts  are  to  be 
met  with. 

The  teeth  of  the  Cestracion  are  fitted  for  the  trituration 
of  hard  substances,  and  for  such  they  are  used,  its  food 
consisting  of  shell-fish,  Ac.  The  teeth  consist  of  vaso-  and 
osteodentine,  protected  by  what  is  apparently  a  structure¬ 
less  layer  of  enamel. 

The  extinct  Cestracionts  extended  far  back  in  time,  being 
met  with  in  palaeozoic  strata,  and  they  were  equally  widely 
distributed  in  space  ;  the  size  of  many  of  the  teeth  also 
indicates  the  existence  of  forms  much  larger  than  the  recent 


THE  TEETH  OF  FISHES. 


237 


timid  and  inoffensive  Cestracion  Philippi.  Many  of  the 
extinct  forms  are  known  only  by  isolated  teeth  ;  of  others 
portions  of  the  jaw  with  teeth  in  situ  have  been  discovered  ; 
thus  fragments  of  the  jaw  of  Acrodus,  the  isolated  fossil 
teeth  of  which  have  been  compared  to  fossil  leeches,  with 
seven  teeth  arranged  in  series,  have  been  met  with. 


Fig.  99  (ff. 


The  Pristis,  or  Saw  fish,  so  far  as  the  mouth  is  concerned, 
is  in  no  way  remarkable,  its  teeth  being  small  and  blunt, 
like  those  of  many  rays.  The  snout  is,  however,  prolonged 
to  an  enormous  length,  and  is  shaped  like  a  gigantic 
spatula,  its  thin  edges  being  beset  by  dermal  spines  of 
large  size,  arranged  at  regular  intervals,  and  implanted  in 
distinct  sockets.  These  dermal  spines,  or  rostral  teeth,  as 
they  are  sometimes  termed,  are  not  shed  and  replaced,  but 
grow  from  persistent  pulps ;  in  structure  they  closely 

(b  Lower  jaw  of  Cestracion  Philippi,  a.  Young  teeth  not  yet  in  use. 
b.  Large  grinding  back  teeth,  c.  Small  pointed  front  teeth. 

The  new  teeth  are  developed  at  the  bottom  of  the  series  on  the  inner 
side,  and,  just  as  in  other  sharks,  are  covered  in  by  a  flap  of  mucous 

membrane. 


238 


A  MANUAL  OF  DENTAL  ANATOMY. 


I 


t  J3.S. 


b _ J 


C... 


resemble  the  teeth  of  Myliobates  (see  page  88),  being  made 

up  of  parallel  denticles,  in  the  centre 
Fig.  100  (1).  0f  each  of  which  is  a  pulp  cavity  or 

medullary  canal. 

What  use  the  Saw-fish  makes  of  its 
armed  snout  is  not  very  certainly 
known,  but  its  rostral  teeth  are  of 
interest  to  the  odontologist  for  several 
reasons — the  one  that  they  are  dermal 
spines,  having  a  structure  all  but 
identical  with  that  of  the  actual  teeth 
of  another  ray,  the  Myliobates ;  the 
other  that  they  are  socketed,  a  manner 
of  implantation  not  at  all  common 
amongst  the  teeth  of  fishes  ;  and  yet 
another,  that  they  grow  from  persistent 
pulps,  also  unusual  in  fishes. 

Broadly  speaking,  the  teeth  of  the 
Bays  (skates)  differ  from  those  of 
typical  sharks  by  being  individually 
blunter,  and  being  more  closely  set 
so  that  they  form  something  approach¬ 
ing  to  a  continuous  pavement  over  the 
jaws,  with  but  little  interspace  left  be¬ 
tween  the  teeth. 

The  dentigerous  surface  of  the  jaw  is 
very  much  rounded,  and  in  some  is 
completely  encased  under  a  pavement 
of  teeth.  Thus,  in  Myliobates,  the 
powerful  jaws  are  straight  from  side 
to  side,  while  their  working  surfaces 


(b  Rostrum  and  under  side  of  the  head  of  a  small  Pristis.  a.  Mouth. 
b.  Rostrum,  c.  One  of  the  rostral  teeth. 

The  teeth,  with  which  the  margins  of  the  jaws  are  covered,  are  so  small 
that  they  cannot  be  represented  in  this  figure. 


THE  TEETH  OF  FISHES. 


239 


from  back  to  front  are  segments  of  a  circle.  The  teeth  form 
a  thick  and  strong  pavement  over  the  jaws,  in  the  manner 
of  their  formation  and  renewal  conforming  with  the  teeth 
of  other  Plagiostomi ;  the  severe  use  to  which  they  are  put 
being  indicated  by  the  extent  to  which  the  grinding  surfaces 
of  those  teeth  which  have  come  into  use  are  worn  down. 

Fig.  101  (b. 


Several  genera  have  the  jaws  thus  covered,  the  number 
of  the  teeth  differing  ;  thus  Myliobates  has  a  central  series  of 
very  broad,  oblong  teeth,  to  the  outer  sides  of  which  are  three 
rows  of  small  hexagonal  teeth  ;  in  (Etobatis  the  large  oblong 
central  plates  constitute  the  whole  armature  of  the  jaw. 

The  structure  of  the  teeth  of  Myliobates  has  already  been 
described  and  figured  (see  page  88). 

(b  Upper  and  lower  jaw  of  Myliobates.  At  a,  the  mosaic  pavement 
formed  by  the  broad  flattened  plates  which  constitute  its  teeth  is  seen, 
these  being  the  oldest  teeth  which  are  about  to  be  shed  off  in  consequence 
of  the  rotation  of  the  whole  sheet  of  mucous  membrane  over  the  surface 
|  of  the  jaws.  The  letter  b  indicates  the  under  surface  of  one  of  the  plates, 
which  is  seen  to  be  finely  fluted  on  its  edge. 


240 


A  MANUAL  OF  DENTAL  ANATOMY. 


Near  the  borderland  between  fish  and  amphibia  is  the 
Lepidosiren,  or  Mud-fish,  which  is  a  fish  rather  than  an 
amphibian.  The  armature  of  its  mouth  is  peculiar,  the 
margins  of  the  lower  jaws  being  formed  by  dental  plates 
anchylosed  to  the  bone.  These  plates  have  upon  their 
edges  five  deep  angular  notches,  the  prominence  of  the 
upper  plate  corresponding  to  the  notches  of  the  lower ; 
and  the  edge  is  kept  somewhat  sharp  by  the  front  surface  - 
being  formed  of  very  dense  hard  dentine,  while  the  bulk 
of  the  tooth  is  permeated  by  large  medullary  canals,  which 
render  it  softer.  The  cutting  plates  of  the  upper  jaw  are 
developed  in  the  median  line  of  the  palate,  and  there  are 
in  front  of  them  conical  piercing  teeth  upon  that  forward 
prolongation  of  the  cartilage  which  takes  the  place  of  a 
distinct  vomer  ;  these  have  sometimes  been  described  as 
being  upon  the  nasal  bone. 

It  would  seem  that  the  two  conical  piercing  teeth  serve 
as  holdfasts,  while  the  cutting  edges  of  the  deeply-notched 
plates  are  brought  into  play  to  slice  up  the  food. 

Both  in  structure  and  general  disposition  the  dental  plates 
in  Lepidosiren  are  paralleled  by  the  teeth  of  Ceratodus,  for 
some  time  known  only  as  a  fossil,  but  of  which  recent 
examples  have  been  captured  near  Queensland ;  this 
resemblance  was  suspected  some  years  ago  by  my  friend, 
Prof.  Moseley,  of  the  Challenger ,  and  has  been  since  worked 
out  by  other  observers. 

Amongst  ganoid  fish  great  diversity  of  dentition  exists. 
Thus  the  sturgeons  have  no  teeth,  the  mouth  being  at  the 
lower  surface  of  the  snout,  and  being  protrusible  as  a  sort  of 
suctorial  tube.  In  the  larval  stages,  however,  the  sturgeon 
possessed  teeth.  In  the  allied  Spatularia  there  are  numerous 
very  minute  teeth,  whilst  there  are  numerous  extinct  ganoids 
with  large  blunt  pointed  teeth  upon  the  palate  and 
mandible. 

Lepidosteus,  the  structure  of  whose  teeth  has  been 


THE  TEETH  OF  FISHES. 


241 


described  on  p.  84,  has  a  long  pointed  snout  furnished  with 
large  sharp  conical  teeth. 

The  Teleostei ,  or  osseous  fish,  form  the  group  which  com¬ 
prises  all  the  fish  most  familiarly  known  to  us,  and  within 
its  limits  the  variation  in  dentitions  is  so  great  that  few,  if 
any,  general  statements  can  be  made  about  them.  It  is  not 
uncommon  to  find  teeth  crowded  upon  every  one  of  the  bones 
which  form  a  part  of  the  bony  framework  of  the  mouth  and 
pharynx,  and  the  teeth  are  sometimes  in  countless  numbers. 
And  such  is  the  variability  that  even  within  the  limits  of 
single  families  great  differences  in  the  teeth  are  to  be  found. 

The  teeth  of  fish  are  of  all  degrees  of  size  and  of  fineness  ; 
in  some  (Chsetodonts)  the  teeth  are  as  fine  as  hairs,  and  are 
so  soft  as  to  be  flexible  ;  they  are  said  to  be  hortiy. 

Teeth  which  are  very  fine  and  very  closely  set  are  termed 
“  dents  en  velours,”  “  ciliiform  ”  or  “  setiform  ;  ”  when  they 
are  a  little  stouter,  “  dents  en  brosse,”  or  “  villiform  ;  ”  and 
when  still  stronger  and  sharper,  “  dents  en  cardes.”  Teeth 
that  are  conical,  wedge-shaped,  spheroidal,  and  lamelliform, 
are  all  to  be  met  with ;  in  fact  there  is  infinite  diversity 
in  the  form  of  fishes’  teeth. 

And  there  are  some  fish,  e.g.,  some  of  the  large  Siluroid 
fishes,  which  have  very  strong,  large  teeth,  an  inch  and  a 
half  or  more  long,  and  very  firmly  anchylosed  to  the  bone. 

The  long  and  very  strong  snout  of  the  Sword  Fish,  formed 
by  a  coalescence  of  maxillary  and  inter-maxillary  bones,  which 
is  able  to  pierce  a  plank,  is  roughened  on  its  lower  surface  by 
villiform  teeth  which  can  be  of  no  use,  and  are  therefore  to 
be  regarded  as  rudimentary  survivals. 

In  the  common  pike  the  mouth  is  crowded  with  sharply- 
pointed  teeth,  having  a  general  inclination  backwards,  and 
being  in  some  parts  of  the  mouth  of  larger  size  than  in 
Dthers.  The  margin  of  the  lower  jaw  is  armed  with  teeth  of 
formidable  size  and  sharpness,  the  smallest  teeth  being  at 
the  front,  where  they  are  arranged  in  several  rows,  and  the 


242 


A  MANUAL  OF  DENTAL  ANATOMY. 


largest  being  about  the  middle  of  the  side  of  the  jaw.  A 
pike,  as  is  well  known  to  anglers,  when  it  has  seized  a  fish 
often  holds  it  across  its  mouth,  piercing  and  retaining  it  by 
means  of  these  largest  teeth  ;  then,  after  holding  it  thus  for  a 
time,  and  so  having  maimed  it  and  lessened  its  power  of  escape, 
it  swallows  it,  generally  head  foremost.  The  tenacity  of  the 
pike’s  hold  is  often  illustrated  when  it  takes  a  bait,  and 
retains  it  so  firmly  that  when  the  angler  “  strikes  ”  the 
hooks  do  not  get  driven  into  the  fish’s  mouth ;  but  after 
tugging  at  the  bait  for  a  time  the  pike  releases  it,  and  the 
angler  finds  that  it  has  never  been  hooked  at  all. 

The  margin  of  the  upper  jaw  is  not  bordered  by  teeth, 
save  at  the  front,  where  the  intermaxillary  bones  carry  a 
few  teeth  of  insignificant  dimensions  ;  indeed,  it  is  rather 
exceptional  for  the  true  maxillary  bones  to  carry  teeth  in 
osseous  fish.  The  roof  of  the  mouth  presents  three  wide 
parallel  bands  of  teeth,  those  in  the  median  band  (on  the 
vomer)  being  directed  backwards,  those  upon  the  lateral 
bands  (on  the  palatine  bones)  backwards  and  inwards. 
Some  of  the  latter  teeth  are  very  large,  but  not  quite  so 
large  as  those  at  the  sides  of  the  lower  jaw. 

The  marginal  teeth  are  firmly  anchylosed,  but  the  teeth 
upon  the  palate  are  all  hinged,  and  in  such  a  manner  that 
they  can  only  bend  exactly  in  one  direction.  Those  of  the 
vomerine  band  which  lie  in  the  middle  line,  will  bend  back¬ 
wards  only ;  those  upon  the  outer  margins  of  this  band 
backwards,  with  an  inclination  outwards.  Those  of  the 
lateral  or  palatine  bands  bend  obliquely  backwards  and 
inwards,  about  at  an  angle  of  45  with  the  median  line  of 
the  mouth,  or  somewhat  more  directly  backwards.  To  a 
body  sliding  over  them  in  one  direction  they  offer  no 
resistance,  bending  down  as  it  passes,  and  springing  up  as 
the  pressure  is  removed  from  them,  but  to  anything  moving 
in  any  other  direction  they  are  rigidly  fixed  sharp  curved 
stakes  impeding  its  further  progress. 


THE  TEETH  OF  FISHES. 


243 


An  elongated  body  of  some  size,  such  as  a  living  fish, 
can  only  be  swallowed  by  the  pike  when  it  is  arranged 


Fig.  102(1). 


lengthwise  in  the  mouth  ;  crosswise  it  cannot  possibly  enter 

(i)  Jaws  of  a  Pike,  viewed  from  the  front,  with  the  mouth  opened  more 
widely  than  is  natural,  so  as  to  bring  the  teeth  into  view.  a.  Group  of 
teeth  situated  on  the  palatine  bone.  b.  Group  of  teeth  situated  on  the 
vomer,  c.  Group  of  teeth  situated  on  the  lingual  bone.  d.  Specially 
large  teeth,  placed  at  intervals  round  the  margin  of  the  lower  jaw. 
e.  Group  of  teeth  on  the  intermaxillary  bones. 

The  diagram  beneath  represents  the  direction  in  which  the  hinged  teeth 
of  the  vomerine  and  palatine  bands  can  bend. 

II  2 


244 


A  MANUAL  OF  DENTAL  ANATOMY. 


the  throat.  The  hinged  teeth  on  the  palate  seem  ad¬ 
mirably  arranged  for  getting  the  fish  into  a  longitudinal 
position  and  keeping  it  there ;  for,  if  we  imagine  the  fish’s 
body  held  up  against  these  teeth,  and  consider  the  direction 
in  which  the  hinging  of  the  teeth  allows  them  to  yield,  it 
will  be  seen  that  every  motion  tending  to  arrange  the  body 
lengthwise,  either  in  the  median  line  of  the  mouth  or  in 
either  of  the  interspaces  between  the  vomerine  and  palatine 
bands  of  teeth,  will  meet  with  no  obstruction,  but  in  every 
deviation  from  this  position  it  will  be  caught  on  the  points  of 
the  teeth  and  resisted.  Thus  with  the  pike’s  mouth  shut, 
and  the  fish  kept  up  against  the  palatine  teeth,  even  its  own 
struggles  will  be  utilised  by  every  movement  tending  to 
place  it  aright  being  allowed,  and  every  other  stopped  by 
the  bands  of  hinged  teeth  entangling  it.  The  structure  of 
these  teeth,  and  the  mechanism  by  which  they  are  rendered 
elastic,  have  been  already  described  (page  217). 

The  lingual  bone,  and  the  three  median  bones  behind  it, 
carry  small  teeth  arranged  in  oblong  patches  ;  the  internal 
surfaces  of  the  branchial  bones  (which  support  the  gills) 
are  armed  with  similar  small  teeth ;  while  the  last  or  fifth 
branchial  arch  (which  carries  no  gills,  the  bones  forming 
it  being  called  inferior  pharyngeal  bones,)  carry  larger 
teeth.  The  superior  pharyngeal  bones  (which  are  median 
portions  of  the  four  anterior  branchial  arches)  also  carry 
recurved  teeth  larger  than  those  which  line  the  rest  of  the 
internal  surfaces  of  each  of  the  branchial  arches. 

The  pike’s  mouth  and  pharynx  thus  fairly  bristle  with 
teeth,  all  directed  somewhat  backwards ;  and  any  one  who 
has  been  unfortunate  enough  to  have  allowed  his  fingers 
to  get  entangled  in  the  mouth  of  a  living  pike  will  realise 
how  small  a  chance  of  its  living  prey  has  of  escape,  when 
once  it  has  been  seized. 

The  teeth  of  the  pike  are  composed  of  a  central  body  of 
osteo-dentine,  on  the  outside  of  which  is  a  layer  in  which 


THE  TEETH  OF  FISHES. 


245 


the  dentinal  tubes  are  directed  towards  the  surface,  as  in 
hard  or  nnvascular  dentine  (see  fig.  48)  ;  while  the  outer¬ 
most  portion  of  all  is  a  very  dense  and  hard,  and  apparently 
structureless,  enamel  film.  The  teeth  are  anchylosed  to  the 
bone,  and  are  very  frequently  renewed,  their  successors 
being  developed  at  one  side  of  their  bases. 

Though  the  pike  has  rather  more  teeth  than  many  other 
fish,  it  may  be  taken  as  a  fair  example  of  most  osseous  fishes 
in  this  respect.  Space  will  only  allow  of  a  few  of  the  more 
exceptional  forms  being  here  described. 

The  angler  (Lophius  piscatorius),  another  predatory  fish, 
with  an  enormous  mouth  and  disproportionately  small  body 
and  tail,  lies  hidden  in  the  mud,  or  crouched  upon  the 
bottom,  and  makes  a  rush  upon  smaller  fishes  which  ap¬ 
proach  sufficiently  near  to  it ;  it  is  remarkable  for  the 
manner  of  attachment  of  the  teeth,  some  of  the  largest  of 
which  upon  the  edges  of  its  jaws  do  not  become  anchylosed, 
but  are  so  attached,  as  has  been  described  at  p.  214,  as  to 
allow  of  their  bending  in  and  towards  the  mouth,  but  not  in 
the  opposite  or  any  other  direction.  The  teeth  of  the  outer 
row  are  firmly  anchylosed  to  the  margins  of  the  jaw,  and  the 
far  larger  hinged  teeth  form  a  sort  of  irregular  second  row. 

The  benefit  of  such  an  arrangement  to  a  fish  of  its  habit 
is  sufficiently  obvious  ;  its  teeth  allowT  the  utmost  freedom  of 
entry,  but  offer  obstacles  to  anything  getting  out  again. 

This  arrangement  of  teeth,  long  supposed  to  be  unique,  is 
closely  paralleled  in  a  very  different  fish,  the  Hake  (Mer- 
lucius,  one  of  the  Gadidfe).  This  fish,  the  most  active  and 
predatory  of  the  Cod  family,  follows  shoals  of  pilchards  and 
of  herrings,  themselves  active  fish,  and  feeds  upon  them. 
The  margins  of  the  jaws  carry  two  distinct  and  regularly 
arranged  rows  of  teeth,  an  outer  smaller  row  which  are 
anchylosed,  and  an  inner  longer  row  vThich  are  hinged. 

|  They  are  very  sharp,  being  tipped  with  spear  points  of 
enamel,  and  are  recurved.  In  the  fresh  state  they  look 


246 


A  MANUAL  OF  DENTAL  ANATOMY. 


quite  red,  being  composed  of  a  richly  vascular  vaso- 
dentine. 

Again,  in  several  of  the  deep  sea  fish  dredged  by  the 


Fig.  103  (>). 


Challenger  from  the  depths  to  which  light  does  not  pene¬ 
trate,  hinged  teeth  have  been  found  (cf.  p.  218).  Many  of 
these  deep  sea  fish  have  very  formidable  dental  armaments, 
and  curiously  enough,  one  of  these,  which  has  exceptionally 
long  upper  teeth,  has  a  downward  projection  from  the  lower 

(l)  Bones  of  the  mouth  of  the  Wolf-fish  (Anarrhicas  lupus).  The  letter 
a.  indicates  the  divergent  pointed  teeth  which  occupy  the  intermaxillary 
bone  ;  the  letter  d.  indicates  the  similar  teeth  which  are  attached  to  the 
front  of  the  mandible,  on  the  middle  and  back  parts  of  which  are  round- 
topped  crushing  teeth  (e).  Strong  crushing  teeth  are  found  also  upon  the 
palatine  bones  {b),  and  upon  the  vomer  (c). 


THE  TEETH  OF  FISHES. 


-247 


jaw,  which  serves  to  protect  them  while  closed,  an  arrange¬ 
ment  elsewhere  only  met  with  in  extinct  mammalia,  such  as 
Dinoceras  and  Machairodus  figured  later  on  in  this  work. 

Another  curious  dentition  is  possessed  by  the  Wolf-fisli 
(Anarrhicas  lupus),  also  an  inhabitant  of  British  waters, 
and  sometimes  to  be  seen  in  London  fishmongers’  shops 
under  the  name  of  the  sea  cat.  The  intermaxillary  teeth 
are  conical,  bluntly  pointed,  and  set  forwards  and  outwards ; 
these  are  antagonised  by  somewhat  similar  teeth  in  the 
front  of  the  lower  jaw.  The  palatine  bones  carry  short, 
bluntly  conical,  or  round  topped  crushing  teeth  in  a  double 
row  ;  the  vomer  is  also  armed  with  a  double  row  of  very 
much  larger  and  shorter  teeth  ;  the  lower  jaw,  with  the 
exception  of  its  anterior  part,  is  occupied  by  teeth  of 
similar  character. 

All  the  teeth  of  the  Wolf-fish  are  anchylosed  slightly  to 
the  bone,  a  definite  process  from  which  forms  a  sort  of  short 
pedestal  for  each  tooth.  The  jaws  are  worked  by  muscles 
of  great  power,  and  it  seldom  happens  that  a  specimen  is 
examined  in  which  some  of  the  teeth  are  not  broken.  It 
feeds  upon  shell  fish,  the  hard  coverings  of  which  are 
crushed  by  the  blunter  teeth,  while  the  pointed  front  teeth 
apparently  serve  to  tear  the  shell  fish  from  the  rocks  to 
which  they  are  commonly  attached. 

In  the  group  of  fish  known  as  “  Gymnodonts  ”  (naked 
toothed),  the  teeth  and  the  margins  of  the  dentigerous  bones 
form  a  sort  of  beak,  which  is  not  covered  by  the  lips.  The 
i  example  here  figured  consists  of  the  upper  and  lower  jaws  of 
the  Diodon,  so  called  because  it  appears  to  casual  observators 
to  have  but  two  teeth.  A  kindred  fish  in  which  the  division 
of  each  jaw  in  the  middle  line  is  conspicuous,  is  similarly 
called  Tetrodon.  The  jaw  consists  of  teeth  and  bone  very 
intimately  fused  together ;  the  broad  rounded  mass  (c.  in 
i  the  figure),  which  lies  just  inside  the  margin  of  the  jaw,  is 
j  made  up  of  a  number  of  horizontal  plates  of  dentine,  the 


248 


A  MANUAL  OF  DENTAL  ANATOMY. 


edges  of  which  crop  out  upon  its  posterior  surface  ;  and 
these  are  united  to  one  another  by  the  calcification  of  the 
last  remains  of  the  pulp  of  each  plate  into  a  sort  of  osteo- 


Fig,  104  d). 


dentine,  the  different  hardness  of  the  two  tissues  keeping 
the  surface  constantly  rough,  as  the  plates  become  worn  away. 
The  whole  margin  of  the  jaw  is  similarly  built  up  of  smaller 
horizontally  disposed  denticles,  or  plates  of  dentine,  which 
are,  as  they  wear  down,  replaced  by  the  development  of 
fresh  plates,  which  are  added  from  beneath,  where  they  are 
developed  in  cavities  situated  low  down  in  the  substance  of 
the  bone. 

The  new  teeth  or  plates  of  dentine  thus  formed  at  the 
base  of  the  hemispherical  masses  within  the  jaws  (at  the 
point  a ),  or  low  down  in  the  substance  of  the  jaw,  do  not 
come  into  use  by  the  ordinary  process  of  displacing  their 
predecessors,  and  being  in  turn  themselves  replaced,  but 

(b  Jaws  of  the  Diodon.  a.  Base  of  the  dental  plates,  where  new  lamella* 
of  dentine  are  being  developed,  b.  Margin  of  jaw,  formed  mainly  by  the 
sides  of  the  denticles,  c.  Compound  tooth,  made  up  of  the  superimposed 
lamellae  of  dentine  anchylosed  together. 


THE  TEETH  OF  FISHES. 


249 


fresh  plates  only  come  into  use  by  the  actual  wearing  away 
of  all  that  is  above  them,  both  dentine  and  bone,  so  that 
they  come  to  be  the  topmost  portion  of  the  jaw.  The 
margins  of  the  jaw  are,  however,  maiidy  built  up  of  dental 
tissues,  there  being  but  little  bone  in  their  interspaces. 

Tetrodon  has  not  the  rounded  triturating  disk  of  the 
Diodon,  or  has  it  but  feebly  represented ;  and  the  margins 
of  the  jaws  are  sharper. 

In  the  parrot-fishes  (Scarus),  which  are  not  very  nearly 
allied  to  the  Gymnodonts,  somewhat  similar  beaks  are  found, 
the  individual  teeth  being  more  conspicuous.  The  whole 
outer  surface  of  the  jaw  near  to  its  working  edge  is  covered 
by  a  sort  of  tesselated  pavement,  formed  by  the  several 
teeth  which  are  pressed  together  into  a  mass,  but  they  form 
only  the  outer  surface  and  the  immediate  edge,  so  that  the 
soft  bone  forms  a  part  of  the  working  surface,  or  would  do 
so  but  that,  by  its  more  speedy  wear,  it  leaves  the  edge, 
formed  by  dentine  and  enamel,  always  prominent  and  more 
or  less  sharp. 

The  structure  and  succession  of  these  teeth  have  been 
carefully  described  by  J.  von  Boas  (Zeits.  f.  Wissen.  Zool. 
xxxii),  and  the  differences  between  the  several  genera 
pointed  out.  He  describes  cementum  as  binding  the 
denticles  together  and  forming  a  part  of  the  working  edge, 
but  that  which  he  describes  as  cementum  appears  to  me  to 
be  that  tissue  which  I  have  termed  “bone  of  attachment.” 
See  page  220. 

In  a  section  of  a  jaw  in  my  possession,  which  I  believed 
to  have  belonged  to  a  Gymnodont  fish  but  which  bears  a 
remarkably  close  resemblance  to  that  figured  by  von  Boas 
as  being  a  jaw  of  Pseudoscarus,  a  very  beautiful  arrange¬ 
ment  serves  to  preserve  the  sharpness  of  the  edge  of  the 
jjaw. 

The  denticles  are  conical,  and  form  a  series  of  hollow 
superimposed  cones  with  the  points  upwards;  they  consist 


250 


A  MANUAL  OF  DENTAL  ANATOMY. 


of  dentine  and  enamel,  and  the  point  of  the  subjacent  cone 
fits  closely  up  into  the  hollow  of  that  above  it,  so  closely 
that  in  von  Boas’  specimen  the  dentine  of  the  older  tooth  is 
in  great  part  absorbed  (?)  to  make  way  for  the  point  of  its 

Fig.  105  (l). 


successor,  so  that  the  working  denticle  comes  to  be  little 
more  than  a  hollow  cone  of  enamel.  This  is  not  the  case  in 
my  specimen  in  which  there  is  a  quantity  of  dentine  left 
in  each  denticle.  This  vertical  series  of  superimposed 
sharp  cones  lie  in  the  midst  of  the  somewhat  thin  jaw  bone, 
fused  together  by  cementum  (?  bone  of  attachment),  and 
enclosed  between  the  inner  and  outer  plates  of  the  jaw. 


(b  Edge  of  jaw  of  Pseudoscarus  (?)  a.  Denticles.  1.  Bone  of  jaw 


THE  TEETH  OF  FISHES. 


251 


The  bone  being  much  softer  than  the  denticle,  wears 
down  much  faster,  so  that  the  edge  is  always  formed  by  a 
prominent  sharp  tooth,  which,  as  the  wearing  down  of  the 
bone  progresses,  falls  off,  and  the  next  one  beneath  it  comes 
into  play.  The  arrangement  recalls  the  way  in  which  a 
scythe  or  a  chisel  is  assisted  in  keeping  its  edge  by  being 
made  of  a  plate  of  steel  welded  between  two  plates  of 
softer  iron. 


The  pharyngeal  bones  are  also  remarkable ;  the  two  lower 
are  united  into  one,  and  the  stout  bone  so  formed  is  armed 
with  teeth  ;  it  is  antagonised  by  two  upper  pharyngeal  bones 
similarly  armed.  It  carries  teeth  which  are  ancliylosed  to 
it,  and  which  are  so  disposed  as  to  keep  the  surface  con¬ 
stantly  rough.  When  they  are  freshly  formed  the  teeth 
have  flattened  thin  edges,  something  like  human  incisors. 
The  teeth  are  coated  with  enamel,  and  thus,  when  calcifi¬ 
cation  has  proceeded  so  far  as  to  obliterate  their  central 
pulp  cavities,  after  the  tooth  is  worn  to  a  certain  point 
(c  in  Fig.  104)  it  presents  a  ring  of  enamel,  inside  which 
comes  a  ring  of  dentine,  and  inside  this  a  core  of  secondary 


(x)  Lower  pharyngeal  hone  of  Pseudoscarus.  a.  Posterior  border,  at 
which  the  teeth  are  unworn,  c.  Oval  areas  formed  by  teeth,  the  points 
)f  which  are  worn  off.  b.  Anterior  edge  of  bone,  at  which  the  teeth  are 
ilmost  completely  worn  away. 


252 


A  MANUAL  OF  DENTAL  ANATOMY. 


dentine,  as  seen  in  the  figure.  Owing  to  the  different  hard¬ 
ness  of  the  three  tissues  a  constant  roughness  of  surface  is 
maintained.  The  upper  pharyngeals  are  similarly  armed  ; 
and  as  the  teeth  and  the  supporting  bone  wear  away,  fresh 
teeth  are  developed  at  the  front,  so  that  the  whole  bone 
undergoes  a  sort  of  gliding  motion  backwards,  the  armature 
of  the  lower  pharyngeal  being  renewed  in  a  similar  manner, 
save  that  new  teeth  and  bone  are  developed  at  its  posterior 
instead  of  its  anterior  extremities. 

The  teeth  are  developed  in  bony  crypts,  beyond  the 
youngest  functional  teeth,  and  perforations  in  the  roofs  of 
the  crypts  give  passage  to  the  connecting  band  between  the 
tooth  sac  and  the  mucous  membrane. 

No  more  fitting  place  will  occur  for  noticing  the  stout 
pharyngeal  teeth  which  are  met  writh  in  so  many  fish. 
Some  fish,  which  are  edentulous  so  far  as  the  mouth  proper  is 
concerned,  have  the  pharyngeal  bones  armed  with  teeth ; 
in  the  carp  and  its  allies,  edentulous  so  far  as  the  mouth 
proper  is  concerned,  the  two  lower  pharyngeal  bones  carry 
long  pointed  teeth,  which  partly  oppose  one  another,  and 
partly  oppose  a  sort  of  horny  tubercle,  wdiich  is  supported 
on  a  process  of  the  base  of  the  occipital  bone. 

A  few  fish  are  quite  without  teeth ;  the  sturgeon,  whose 
mouth  forms  a  protrusible  sucker,  is  edentulous,  as  are  also 
the  pipe  fish,  and  the  little  sea  horse  (Hippocampus),  now  so 
common  in  aquaria. 

But  as  a  rule  fish  are  remarkable  for  the  great  number  of 
their  teeth,  which  are  being  constantly  shed  off  and  replaced 
bv  successors  an  indefinite  number  of  times. 

In  all  the  fish  hitherto  mentioned  in  these  pages,  it 
happens  that  the  teeth  in  different  parts  of  the  mouth  differ 
in  size  and  in  the  function  which  they  have  to  perform ; 
but  this  is  only  so  because  a  few  striking  forms  have  been 
naturally  selected  for  description.  It  is  far  commoner  for 
all  the  teeth  of  a  fish,  particularly  of  those  fish  which  have 


THE  TEETH  OF  FISHES. 


253 


countless  numbers  of  teeth,  to  be  very  nearly  alike  in  form 
and  size  in  all  parts  of  the  mouth.  As  a  general  rule,  fish 
do  not  comminute  their  food  very  fully,  but  make  use  of 
their  teeth  simply  for  the  prehension  of  prey,  not  sub¬ 
mitting  the  food  to  any  mastication  whatever  ;  their  teeth 
are  hence  often  mere  sharp  cones,  slightly  recurved,  or  set 
looking  backwards.  Thus,  though  the  mouth  of  the  common 
pike  is  beset  with  an  immense  number  of  sharp  teeth,  its 
food  is  swallowed  whole,  and  very  often  is  alive  when  it 
reaches  the  stomach,  the  sole  purpose  served  by  the  teeth 
being  the  prevention  of  its  escape  when  once  it  has  been 
seized. 

Implantation  of  the  teeth  in  sockets  is  not  usual  in  the 
dass  of  fish,  but  it  does  occur  ;  for  example  the  Barracuda 
fike  (Sphyrmna)  has  its  lancet-shaped  teeth  implanted  in 
listinct  sockets,  to  the  Avails  of  which  they  are  said  to 
>ecome  slightly  anchylosed ;  the  file-fish  and  others  might 
dso  be  cited.  And  although  the  succession  of  teeth  is 
lsually  from  the  side,  in  some  cases  the  successional  teeth 
.re  developed  in  alveolar  cavities  Avithin  the  substance  of 
he  bone,  and  displace  their  predecessors  in  a  vertical  direc- 
ion,  as  happens  in  the  pharyngeal  teeth  of  the  Wrasses,  or 
he  curiously  human-looking  incisors  of  the  Sheep’s  head  fish 
Sargus)  ;  the  Lepidosteus  also  has  its  teeth  affixed  in  incom¬ 
plete  sockets,  to  the  Avails  of  which  they  are  anchylosed  ; 
his  is  not  a  very  uncommon  arrangement  with  the  teeth  of 
sh  when  they  are  socketed  at  all. 

It  is  not  common  for  sexual  differences  to  be  met  with 
etAveen  the  teeth  of  the  male  and  female,  though  a  slight 
ifference  exists  between  the  sexes  in  some  species  of  Skate. 
,nd  although  not  strictly  speaking  a  dental  character,  it 
iay  not  be  out  of  place  to  mention  here  the  peculiar 
|:mature  of  the  jaw  of  the  male  Salmon  at  the  breeding 
Lason. 

[  The  end  of  the  lower  jaAV  becomes  produced,  and  turned 


m.  H.  WALTER 


254 


A  MANUAL  OF  DENTAL  ANATOMY. 


upwards  at  its  point ;  the  stout  cartilaginous  hook  thus 
formed  is  of  such  dimensions  that  it  has  to  be  accommo¬ 
dated  during  closure  of  the  mouth  in  a  deep  cavity  formed' 
for  it  between  the  intermaxillary  bones.  In  some  Canadian 
salmon  this  process  is  supposed  to  be  constant  in  the  older 
males,  but  in  the  British  fish  it  disappears,  and  only  exists 
at  the  breeding  season.  A  fish  in  which  it  is  strongly 
developed  is  a  foul  fish,  and  is  called  a  Kelt.  It  is  used 
apparently  as  a  battering  ram,  and  such  salmon  are  con¬ 
stantly  found  killed,  with  their  sides  deeply  gashed  by  the 
charges  of  their  opponents. 

Not  much  can  be  said  in  general  terms  of  the  structure 
of  the  teeth  of  fish.  The  bulk  of  the  teeth  of  most  fishes 
is  made  up  of  one  or  other  modification  of  vasodentine  or 
osteodentine ;  this  is  often  glazed  over  upon  its  exterior  by 
a  thin  film  of  enamel,  so  thin  as  often  to  appear  structure¬ 
less. 

Unvascular  dentine  also  forms  the  teeth  of  many  fish, 
and  in  some  is  remarkable  for  the  fineness  of  its  tubes ;  in 
fact,  every  form  of  dentine,  from  fine-tubed  hard  dentine 
to  tissue  indistinguishable  from  coarse  bone  is  to  be  found 
in  this  class. 

Dentine  of  very  complex  structure  (labyrintho-dentine) 
is  met  with  in  some  fish ;  and  an  example  from  the  Lepi- 
dosteus  (American  garpike,  a  ganoid  fish)  has  been  figured  at 
page  82. 

Enamel  is  often  present  in  a  very  thin  layer,  glazing 
the  exterior  of  the  dentine  (see  Fig.  49);  sometimes  it 
forms  a  mere  tip,  a  sort  of  spear-point  to  the  tooth  as  in 
the  Eel  and  the  Hake  (see  Figs.  93  and  89),  and  sometimes 
it  is  very  thick,  and  itself  permeated  by  systems  of  tubes 
(see  Fig.  25). 

Cementum  is  of  comparatively  rare  occurrence  in  fish. 

Professor  Kolliker  has  shown  that  in  a  very  large  number 
of  fishes  the  skeleton  more  nearly  resembles  dentine  than 


THE  TEETH  OF  FISHES. 


255 


.1 


I 


true  bone  in  its  structure ;  whilst  the  dermal  scales  and 
protective  spines  of  fish  are  often  made  up  of  a  tissue  much 
resembling  dentine  (cf.  Professor  Williamson,  Philos.  Trans. 
1849).  We  may  say,  then,  that  just  as  in  the  external  skin, 
bony  or  dentinal  plates  are  developed  for  the  purpose  of 
protecting  it  from  destruction  by  attrition,  so  for  a  similar 
purpose  teeth  are  developed  in  that  portion  of  the  mucous 
membrane  which  covers  the  jaws. 


CHAPTER  VII. 


THE  TEETH  OF  BATRACHIA  AND  REPTILES. 

In  these  classes  the  teeth  are  never  so  numerous  nor  so 
widely  distributed  upon  the  bones  of  the  mouth  as  in  fish ; 
a  double  row  of  teeth  arranged  in  concentric  lines  in  the 
upper  jaw,  between  which  a  single  row  of  teeth  upon  the 
lower  jaw  passes  when  the  mouth  is  closed,  is  an  arrange¬ 
ment  rather  common  amongst  Batrachia.  The  outer  of  the 
two  rows  of  teeth  in  the  upper  jaw  is  situated  upon  the 
premaxillary  and  maxillary  bones,  and  usually  extends 
further  back  than  the  vomerine  or  inner  row.  Almost  all 
Batrachians  and  Reptiles  have  an  endless  succession  of 
teeth  ;  but  there  are  a  few  lizards  (e.g.,  Hatteria),  in  which 
the  manner  of  succession,  if  there  be  any,  has  not  been 
definitely  ascertained. 

From  this  type  of  dentition  there  are  many  deviations ; 
thus  the  toads  are  edentulous,  and  the  frog  has  no  teeth  in 
the  lower  jaw. 

The  teeth  of  the  frog  form  a  single  row  upon  the  margin 
of  the  upper  jaw,  their  points  projecting  but  little  above 
the  surface  of  the  mucous  membrane,  and  the  vomerine 
teeth  are  few  in  number  and  cover  only  a  small  space. 

The  edentulous  lower  jaw  passes  altogether  inside  the 
row  of  upper  teeth,  and,  having  rounded  surfaces  and  no  lip, 
fits  very  closely  against  the  inner  sides  of  the  teeth.  Thus 
it  leaves  very  little  room  for  the  young  developing  tooth 
sacs,  which  are  accommodated  with  the  space  required  for 


THE  TEETH  OF  REPTILES, 


257 


the  attainment  of  their  full  size,  by  the  absorption  of  the 
older  solid  bone  and  the  tooth  which  has  preceded  them, 
in  the  following  manner.  The  teeth  are  attached  to  the 
bone  by  anchylosis,  each  tooth  being  perched  upon  a  little 
pedestal  of  bone  which  is  specially  formed  for  it ;  and  the 
successional  teeth,  the  germs  of  which  originally  lay  at 
the  inner  sides  of  the  old  teeth,  commonly  undermine  the 
side  of  the  pedestals  and  the  bases  of  the  latter,  and  move 
bodily  beneath  them,  so  that  the  new  tooth  completes 
its  development  in  what  was  once  the  pulp  cavity  of  its 
predecessor. 

The  teeth  of  the  frog  consist  of  a  body  of  hard  dentine, 
coated  with  an  exceedingly  thin  layer  of  enamel,  the  exist¬ 
ence  of  which  has  been  doubted  by  some  writers  ;  but  a 
study  of  the  tooth-sac  of  the  animal  renders  it  probable  that 
the  transparent  layer  which  is  undoubtedly  there  is  really 
enamel. 

The  teeth  of  the  newt  and  its  ally  the  salamander  are 
)  remarkable  for  having  tips  of  enamel,  somewhat  like  those 
of  the  eel  (see  Fig.  93),  save  that  they  are  bifurcated,  the 
one  point  being  larger  and  longer  than  the  other. 

The  tadpole  has  its  jaws  armed  with  tough  horny  plates 
something  like  a  turtle’s  bill,  which  are  shed  off,  prior  to 
the  development  of  any  true  teeth ;  at  all  events  I  have 
myself  been  unsuccessful  in  discovering  any  tooth  germs  at 
the  period  when  its  horny  bills  are  still  in  use,  but  Dr. 
Beard  states  that  the  horny  teeth  of  amphibian  larvee  are 
secondary  developments. 

Some  extinct  batrachia  were  of  large  size ;  the  Laby- 
•inthodon,  the  structure  of  whose  teeth  has  already  been 
lescribed  (page  85),  was  furnished  with  a  marginal  row  of 
:eeth  in  the'  upper  jaw,  of  which  some  few  were  of  larger 
|;ize  and  greater  length  than  the  others.  In  the  lower  jaw, 

I  he  teeth,  which  are  similar  to  those  of  the  upper,  are 
disposed  in  some  sense  in  an  incomplete  double  row,  the 


258 


A  MANUAL  OF  DENTAL  ANATOMY. 


series  of  smaller  teeth  not  being  interrupted  by  the  occur¬ 
rence  of  the  larger  tusks,  but  passing  in  unbroken  series 
outside  them.  The  Labyrinthodon  was  possessed  also  of 
palatine  teeth. 

The  teeth  were  anchylosed  to  slight  depressions  or  sockets, 
and  the  successional  teeth  w^ere  probably  developed,  as  in 
the  frog,  at  the  inner  side  of  the  bases  of  the  teeth  already  in 
position,  as  there  are  no  indications  of  crypts  within  the 
bone. 

In  many  reptiles  teeth  are  developed  for  the  merely  tem¬ 
porary  end  of  effecting  an  exit  from  the  egg-shell.  This 
purpose  is  sufficiently  answered  by  the  hard  snout  of  the 
crocodiles,  and  by  a  sort  of  snout  developed  in  Chelonia,  but 
snakes  and  lizards  have  sharp  teeth,  which  afterwards  are 
lost,  developed  on  the  premaxillary  bones  (Owen). 

The  Chelonia,  comprising  the  Tortoises  and  Turtles,  have 
no  teeth,  but  the  margins  of  the  jaws  are  sheathed  in  horny 
cases,  which  are  variously  shaped  in  accordance  with  the 
habit  of  the  animal,  being  sharp  and  thin  edged  in  carni¬ 
vorous,  and  blunt  and  rugged  in  herbivorous  species. 

Saurian  reptiles  (lizards,  &c.),  have,  as  a  rule,  rather 
simple  teeth,  which  are  confined  to  the  margin  of  the  jaws, 
the  occurrence  of  palatal  teeth  being  less  usual.  The 
teeth  are  of  various  forms,  being  blunt  and  rounded  in  many 
genera,  whilst  in  others  they  are  long  and  pointed.  They 
are  generally  made  up  of  a  central  body  of  hard  dentine, 
more  or  less  completely  invested  by  a  cap  of  enamel ;  and 
they  are  attached  to  the  bone  by  anchylosis. 

When  the  tooth  is  anchylosed  by  its  outer  side  to  an 
external  parapet  of  bone,  the  creature  is  said  to  be  “  pleu- 
rodont,”  when  by  the  end  of  its  base  it  is  attached  to  the 
summit  of  a  parapet  it  is  “  acrodont.” 

The  succession  of  teeth  in  the  Lizards  is  constant,  new 
teeth  being  developed  at  the  inner  side  of  the  bases  of  the 
old  teeth,  which  become  undermined  by  absorption  and  fall 


THE  TEETH  OF  REPTILES. 


259 


off  when  the  successional  tooth  has  attained  to  a  certain 
stage  in  its  development. 

The  accompanying  figure  of  the  lower  jaw  of  a  Monitor 
lizard  will  give  an  idea  of  a  dentition  common  in  the 
group.  The  teeth  are  not  very  large  nor  very  numerous, 
there  being  about  30  in  the  jaw ;  towards  the  front  of  the 


Fig.  107  f1)- 


mouth  they  are  a  little  more  pointed  than  at  the  back,  but 
the  differences  in  this  respect  are  not  striking. 

At  the  inner  side  of  the  bases  of  the  teeth  are  seen 
foramina  which  lead  into  the  spaces  in  which  new  teeth  are 
being  developed. 

Amongst  the  lizards  considerable  variety  in  the  form  of 
the  teeth  themselves  exists,  some  having  thin  serrated 
j  edges,  others  being  exceedingly  blunt  and  rounded,  but  in 
the  general  disposition  of  the  teeth  there  is  considerable 
uniformity. 

The  teeth  of  some  lizards  consist  at  their  apices  of  ordinary 
hard  dentine,  with  a  simple  central  pulp  cavity,  but  at 
their  bases  of  plicidentine  with  numerous  subdivisions  of 
:he  pulp  cavity,  as  is  seen  in  the  Monitor  lizards  (Varanus, 
see  p.  83).  One  Mexican  lizard  (Helodermus)  has  the  re- 

I 

p)  Lower  jaw  of  a  Lizard  (Varanus  Gfouldii).  a.  Foramina  leading  to 
avities  of  reserve  ‘  r  ■ 1  < 


260 


A  MANUAL  OF  DENTAL  ANATOMY. 


putation  of  being  poisonous,  and  has  teeth  which  are 
grooved  both  back  and  front ;  but  it  is  doubtful  whether  its 
harmful  powers  have  not  been  exaggerated.  In  Heloderma 
the  salivary  glands  of  the  lower  jaw,  probably  the  sub¬ 
maxillary  glands,  lie  close  against  the  under  side  of  the  bone. 
In  a  dissection  made  by  Professor  Stewart  upon  a*  specimen 
in  the  College  of  Surgeons  museum,  there  appear  to  be  a 
number  of  ducts  which  seem  to  actually  perforate  the  bone, 
and  they  emerge  by  series  of  little  holes  which  lie  in  the 
sulcus  between  the  lip  and  the  teeth,  close  to  the  necks  of 
the  teeth. 

In  the  Python  the  corresponding  gland  also  has  many 
ducts  which  open  in  a  similar  position,  but  they  attain  to  it 
without  any  perforation  of  the  bone,  and  there  is  no  reason 
to  suppose  that  their  secretion  is  at  all  poisonous  ;  in  the 
case  of  Heloderma  there  is,  however,  no  doubt  that  the 
secretion  is  poisonous ;  indeed  the  bite  of  a  specimen  in 
the  Zoological  Gardens  has  been  found  to  be  fatal  to  small 
animals,  and  Dr.  Weir  Mitchell  states  that  in  one  instance 
it  is  known  to  have  been  fatal  to  man.  It  is,  however,  a 
creature  of  gentle  disposition,  and  it  is  not  at  all  easy  to 
make  it  bite. 

Yaso-dentine  occurs  in  the  teeth  of  some  saurians,  as 
for  example,  in  those  of  the  great  extinct  Iguanodon,  in 
which  it,  roughly  speaking,  formed  the  inner  half  of  the 
crown,  the  outer  moiety  consisting  of  hard  dentine.  In 
addition  to  this  peculiarity,  the  teeth  of  Iguanodon  were 
remarkable  for  the  partial  distribution  of  the  enamel,  which 
was  strongly  ridged,  the  ridges  being  serrated,  and  was  con¬ 
fined  to  the  outer  side  of  the  crown.  Thus  at  the  outside 
came  the  hardest  tissue,  the  enamel ;  next  the  harder  dentine, 
and  on  the  inside,  the  softer  vaso-dentine.  Hence,  as  the 
tooth  wore  down,  a  sharp  edge  was  long  preserved. 

There  is  a  New  Zealand  lizard,  to  which  the  several  names 
of  Hatteria,  Sphenodon,  and  Rhyncocephalus  have  been  given, 


THE  TEETH  OF  REPTILES. 


261 


which  has  a  very  peculiar  dental  armature  (Dr.  Gunther, 
Phil.  Trans.,  1867). 

The  intermaxillary  bones  are  armed  with  two  teeth,  so 
large  as  to  be  co-extensive  with  the  whole  bone  in  width, 
and  of  a  ’form  which  recalls  that  of  the  gnawing  incisors 
of  Rodents  ;  the  other  teeth  are  quite  small,  and  “  acrodont  ” 
in  their  attachment. 

But  the  great  peculiarity  of  Hatteria  is  that  the  alveolar 
margins  of  the  jaws  are  sharp,  and  when  the  teeth  are  worn 
down,  which  would  happen  in  adult  specimens,  the  actual 
sharp  margins  of  the  bone  come  into  play  '  as  masticatory 
organs,  near  to  the  front  of  the  mouth.  It  occurred  to  me 
as  probable  that  the  surface  thus  exposed  might  be  coated 
with  dentine,  but  a  microscopic  examination  of  one  of  the 
specimens  in  the  British  Museum,  which  I  was,  by  the 
kindness  of  Dr.  Gunther,  enabled  to  make,  proved  that  the 
dense  ivory-like  surface  which  serves  the  purposes  of  masti¬ 
cation  is  true  bone,  and  has  no  relation  to  dental  structure. 

There  are  very  few  other  instances  of  actual  bone, 
uncoated  by  dental  tissues,  being  used  for  masticatory 
purposes. 

The  great  extinct  Dicynodon,  an  African  fossil,  also 
had  sharp  trenchant  margins  to  its  jaws ;  it  is  not 
known  whether  these  were  sheathed  in  horny  cases  like 
those  of  the  turtles,  or  whether  the  bones  themselves  came 
into  use,  as  in  Hatteria.  But  the  most  striking  peculiarity 
of  Dicynodon  was  the  co-existence  with  such  jaws  of  a  pair 
if  very  large  caniniform  tusks,  a  thing  very  unusual  in 
:he  reptilian  class,  extending  downwards  and  forwards  from 
:he  upper  jaw,  and  growing  from  persistent  pulps. 

The  dentition  of  Ophidian  reptiles  (snakes)  is  very  uni- 
orm ;  they  may  be  conveniently  divided  into  two  groups, 
he  poisonous  and  the  noil-venomous  snakes. 

N on-venomous  snakes  have  one  row  of  teeth  in  the  lower 
aw,  and  two  rows  in  the  upper  jaw;  in  the  latter  the 


262 


A  MANUAL  OF  DENTAL  ANATOMY. 


maxillary  bones  carry  one  row,  while  a  parallel  internal  row 
is  supported  upon  the  palatine  and  pterygoid  bones. 

The  teeth  are  in  both  groups  strongly  recurved,  and  are 
firmly  anchylosed  to  the  bone  ;  they  consist  of  a  central 
body  of  unvascular  dentine,  coated  by  a  very  thin  layer  of 
enamel  (there  is  not,  as  is  generally  supposed,  any  layer  of 
cementum,  the  enamel  having  been  erroneously  supposed  to 
be  such). 

The  two  halves  of  the  lower  jaw  are  connected  at  the 
symphysis  by  an  exceedingly  elastic  ligament ;  their  articu¬ 
lation  with  the  base  of  the  skull  through  the  medium  of  an 
elongated  movable  quadrate  bone,  is  also  such  as  to  allow 
of  their  being  widely  separated  from  the  skull  and  from  one 
another,  which  allows  of  the  ddatation  rendered  necessary  by 
the  large  size  of  the  creatures  which  a  snake  swallows  whole. 

The  teeth  of  the  snake  are  simply  available  for  seizing 
prey  and  retaining  it,  as  the  snakes  invariably  swallow  their 
prey  whole,  and  in  no  sense  masticate  it. 

As  the  object  to  be  swallowed  is  often  so  disproportionately 
large  as  to  make  the  process  of  deglutition  appear  an  im- 
jDOssibility,  the  mouth  and  pharynx  have  to  undergo  great 
dilatation.  The  arrangements  which  combine  to  give  to  the 
lower  jaw  its  mobility  have  just  been  alluded  to ;  the 
successional  tooth  germs,  which  are  very  numerous,  are 
also  arranged  in  the  snake  in  an  unusual  position,  which  by 
bringing  them  very  close  to  the  surface  of  the  bone,  to 
which  they  lie  parallel,  renders  them  less  liable  to  displace¬ 
ment  and  injury  than  they  would  have  been  had  they  been 
placed  vertically,  as  they  are  in  all  other  creatures ;  while 
in  addition  to  the  advantage  of  protection  by  position,  they 
are  wrapped  round  by  a  sort  of  adventitious  capsule  of  con¬ 
nective  tissue. 

As  the  teeth  during  their  development  are  thus  lying  down 
parallel  with  the  length  of  the  jaw-bone,  when  the  period 
for  their  replacing  a  predecessor  arrives,  they  have  not  only 


THE  TEETH  OF  REPTILES . 


263 


to  move  upwards,  but  also  to  become  erected  ;  how  this 
is  done  remains  a  mystery,  for  I  have  been  quite  unable  to 
discern  the  means  by  which  it  is  accomplished. 


When  a  snake  has  seized  its  food,  which  it  retains  by 
means  of  its  many  sharp  recurved  teeth,  it  slowly  swallows 
it  by  advancing  first  its  lower,  then  its  upper  jaw,  till  it 
thus,  so  to  speak,  forces  itself  over  the  body  of  its  prey. 
When  this  latter  is  large,  deglutition  is  a  very  lengthy 
I  process,  but  an  English  snake  can  swallow  a  moderate-sized 
j  frog  with  considerable  rapidity. 

C1).  Developing  teeth  of  a  Snake.  /.  Oral  epithelium,  e.  Neck  of  the 
■  enamel  organs,  b.  Dentine  pulp.  c.  Enamel  cells,  d.  Dentine.  1,  2. 
Very  young  germs.  3,  4.  Older  germs. 


234 


A  MANUAL  OF  DENTAL  ANATOMY. 


There  is  an  African  snake  (Rachiodon)  which  has  none  but 
rudimentary  teeth  •  its  food  consists  of  eggs,  which  thus 
escape  breakage  until  they  reach  the  oesophagus,  into  which 
spinous  processes  from  the  under  surface  of  the  vertebrae 
project,  and  there  serve  to  break  the  egg ;  snakes  with 
their  dentitions  similarly  modified  exist  also  in  India  (e.g., 
Elachistodon). 

Fig.  109  (*). 


It  has  already  been  mentioned  that  the  non-venomous 
snakes  have  two  complete  rows  of  teeth  in  the  upper  jaw, 
the  outer  row  being  situated  on  the  maxillary  bones,  the 
inner  upon  the  palatine  and  pterygoid  bones.  The  teeth  of 
such  snakes  as  the  Pythons -are  all  simple  recurved  cones, 

P)  One  half  of  the  skull  of  a  Python  (without  the  lower  jaw)  seen  from 
below,  a.  Intermaxillary  bone.  b.  Maxillary  bone,  carrying  the  outer 
row  of  teeth,  c.  cl.  Palatine  bone  and  pterygoid  bone,  the  teeth  upon 
which  constitute  the  inner  or  secon'd  row  of  teeth. 


THE  TEETH  OF  REPTILES. 


265 


and  are  none  of  them  either  grooved  or  canaliculated.1 
Some  of  the  harmless  snakes,  however,  have  particular 
teeth  which  are  developed  to  a  greater  length  than  the  rest, 
and  others  have  the  posterior  teeth  on  the  maxillary  bones 
grooved  ;  but  the  statement  that  this  grooving  serves  to 
convey  an  acrid  saliva  into  the  wound  inflicted  rests  on  in¬ 
sufficient  foundation.  The  poisonous  snakes  are  charac¬ 
terized  by  a  shortening  of  the  series  of  teeth  carried  upon 
the  maxillary  bone,  and  by  the  front  teeth  of  the  series  being 
developed  to  much  greater  length  than  those  which  lie 


Fig.  110  (2). 


behind  it.  Thus  Hydrophis,  a  genus  of  poisonous  sea-snakes, 
has  five  or  more  teeth  upon  the  maxillary  bone,  the  fore¬ 
most  of  which  is  much  the  largest,  and  this  largest  tooth  is 
so  deeply  grooved  upon  its  anterior  surface  as  to  be  converted 
into  a  tube,  the  tube  serving  to  convey  the  poison  into  the 
wounds  inflicted  by  it. 

(1)  It  has  been  proposed  to  divide  the  Ophidia  into  groups,  distinguished 
by  the  presence  or  absence  of  grooved  teeth,  thus  : — 

i.  Aglyphodontia.  No  grooved  or  canaliculated  maxillary  teeth. 

ii.  Opisthoglyphia.  Some  of  the  posterior  maxillary  teeth  grooved. 

iii.  P voter  oglyphia.  Anterior  maxillary  teeth  grooved. 

Posterior  maxillary  teeth  solid. 

iv.  Solenoglyphia.  Maxillary  teeth  few,  canaliculated — poisonous 

snakes. 

(2)  Head  and  jaws  of  Hydrophis.  The  maxillary  bone  ( b ),  instead  of 
carrying  a  complete  series  of  teeth,  is  armed  with  a  few  teeth  only  near  to 
the  front.  The  foremost  tooth  is  canaliculated,  and  forms  the  poison  fang. 


266 


A  MANUAL  OF  DENTAL  ANATOMY. 


Poisonous  snakes  which  have  several  teeth  upon  the 
maxillary  bone  for  the  most  part  present  some  little  external 
resemblance  to  the  harmless  snakes,  and  are  called  “  colu- 
brine  poisonous  snakes  ”  (coluber  being  the  name  of  a  genus 
of  harmless  snakes) ;  they  present  transitional  characters 
between  these  and  the  more  specialised  or  “  viperine  ”  poison¬ 
ous  snakes.  The  Cobra  is  a  familiar  example  of  a  colubrine 
poisonous  snake,  and  almost  all  the  venomous  snakes  of 
Australia  belong  to  this  group.  Their  poison  fangs  are  not 
very  long,  and  they  remain  constantly  erect,  the  maxilla  to 
which  they  are  anchylosed  not  being  movable,  as  in  the 
viperine  snakes  :  it  also  carries  a  varying  number  of  small 
insignificant  teeth  behind  the  poison  fang. 

In  the  viperine  poisonous  snakes  (Puff-Adder,  Eattle- 
snake,  Vipers,  Ac.,)  the  poison  apparatus  is  yet  more 
specialised.  The  maxillary  bone  carries  no  teeth  at  all 
behind  the  poison  fang ;  it  is  so  reduced  in  length  as  to  be 
of  squarish  form,  and  is  so  articulated  to  the  skull  as  to  be 
movable. 

The  poison  fang  is  of  great  length,  so  that  if  constantly 
erect  it  would  be  much  in  the  way ;  when  it  is  out  of  use, 
however,  it  is  laid  flat  along  the  roof  of  the  mouth,  and  is 
only  erected  for  the  purpose  of  striking ;  when  in  repose  it 
is  altogether  hidden  by  a  fold  of  mucous  membrane,  which, 
when  it  is  erected,  becomes  tightly  stretched  over  a  part  of 
its  anterior  surface,  and  serves  to  direct  the  poison  down 
the  poison  canal  by,  to  a  great  extent,  preventing  its  escape 
around  the  exterior  of  the  tooth. 

The  mechanism  by  which  the  poison  fang  is  erected  is 
thus  described  by  Professor  Huxley  (Anatomy  of  Verte- 
brated  Animals,  p.  241): — “When  the  mouth  is  shut  the 
axis  of  the  quadrate  bone  is  inclined  downwards  and  back¬ 
wards.  The  pterygoid,  thrown  back  as  far  as  it  can  go, 
straightens  the  ptery go-palatine  joint,  and  causes  the  axis 
of  the  palatine  and  pterygoid  bones  to  coincide.  The  trans- 


THE  TEETH  OF  REPTILES. 


267 


verse,  also  carried  back  by  the  pterygoid,  similarly  pulls  the 
posterior  part  of  the  maxilla  and  causes  its  proper  palatine 
face,  to  which  the  great  channeled  poison  fangs  are  attached, 
to  look  backwards.  Hence  these  fangs  lie  along  the  roof  of 
the  mouth,  concealed  between  folds  of  the  mucous  mem¬ 
brane.  But  when  the  animal  opens  its  mouth  for  the 
purpose  of  striking  its  prey,  the  digastric  muscles,  pulling 
up  the  angle  of  the  mandible,  at  the  same  time  thrust  the 
distal  end  of  the  quadrate  bone  forwards.  This  necessitates 


Fig.  Ill  O. 


the  pushing  forward  of  the  pterygoid,  the  result  of  which 
is  twofold  :  firstly,  the  bending  of  the  ptery go-palatine  joint; 
secondly,  the  partial  rotation  of  the  maxillary  upon  its 
lachrymal  joint,  the  hidden  edge  of  the  maxillary  being 
thrust  downwards  and  forwards. 

“  In  virtue  of  this  rotation  of  the  maxillary  through  about 
a  quarter  of  a  circle,  the  dentigerous  face  of  the  maxilla 
looks  downwards  and  the  fangs  are  erected  into  a  vertical 
position.  The  snake  1  strikes  5  by  the  simultaneous  contrac- 

f'1)  Side  and  front  view  of  the  skull  of  Craspedocephalus  melas.  A 
bristle  is  passed  down  the  poison  canal.  Mx.  Maxillary  bones.  Mn. 
Mandible.  PI.  Palatine  bones.  Pt.  Pterygoid  bones.  Qu.  Quadrate 
bone.  T.  Transverse  bone. 

A.  Side  view. 


B.  Front  view. 


268 


A  MANUAL  OF  DENTAL  ANATOMY. 


tion  of  the  crotaphite  muscle,  part  of  which  extends  over 
the  poison  gland,  the  poison  is  injected  into  the  wound 
through  the  canal  of  the  fang,  and  this  being  withdrawn, 
the  mouth  is  shut,  all  the  previous  movements  reversed, 
and  the  parts  return  to  their  first  position.” 

The  poison  fang  is  a  long,  pointed,  slightly  recurved  tooth, 
traversed,  by  a  canal  Avhich  commences  on  its  front  surface, 
near  to  the  bone,  and  terminates  also  on  its  front  surface,  a 
little  distance  short  of  its  point ;  in  the  figure  a  bristle  has 
been  passed  through  it,  and  shows  the  points  where  it  com¬ 
mences  and  terminates.  This  tube  conveys  the  poison  into 
the  puncture,  its  upper  orifice  being  in  close  relation  with 
the  end  of  the  duct  of  the  poison  gland. 

It  has  been  mentioned  that  some  snakes  which  have  not 
definite  poison  fangs  have  a  few  of  the  large  posterior  teeth 
grooved  upon  their  front  surfaces,  the  object  of  this  grooving 
being,  as  a  matter  of  conjecture,  to  convey  a  more  or  less 
poisonous  saliva  into  the  wounds  inflicted  by  them. 

By  imagining  such  an  anterior  groove  to  be  deepened, 
and  finally  converted  into  a  canal  by  its  edges  growing  up 
and  meeting  over  it,  we  shall  have  a  fair  conception  of  the 
nature  of  the  tube  in  a  poison  fang,  which  is  thus  really 
outside  the  tooth  ;  which  might  thus,  at  least  in  its  canali- 
culated  part,  be  regarded  as  a  thin  flattened  tooth  bent  round 
so  as  to  form  a  tube.  Just  as  there  are  gradations  in  the 
armature  of  the  maxillary  bone,  which  link  together  the 
extreme  form  of  the  harmless  Python,  and  the  venomous 
Rattlesnake,  so  there  are  gradations  in  the  form  of  the 
poison  tooth,  in  the  degree  in  which  the  groove  is  converted 
into  a  canal. 

In  colubrine  poisonous  snakes  the  canal  is  visible  on  the 
exterior  of  the  tooth,  where  an  apparent  fissure  marks  the 
point  where  the  two  lips  of  the  groove  have  met.  Thus  the 
poison  fang  of  Hydrophis,  although  in  a  part  of  its  length 
the  canal  is  quite  closed  in,  has  a  vejy  marked  line  along 


THE  TEETH  OF  REPTILES. 


269 


its  front)  and  in  section  it  looks  much  as  would  the  dentine 
in  Fig.  112,  if  the  two  cornua  had  their  rounded  extremities 
brought  together  into  actual  contact,  without,  however, 
their  rounded  outline  being  altered. 

But  in  the  poison  fang  of  a  viperine  snake  the  lips  of  the 
groove  are  flattened  and  fitted  to  one  another,  so  that  not  a 
vestige  of  the  join  can  be  seen  upon  the  smooth  exterior 
of  the  tooth.  In  the  following  figure  the  pulp  cavity  is 

Fig.  112  C1). 


seen  to  be  a  thin  flattened  chamber  partly  surrounding  the 
tube  formed  for  the  conveyance  of  the  poison. 

The  poison-fang  is  exceedingly  sharj),  its  point  being  con¬ 
tinued  some  little  distance  beyond  the  place  where  the 
poison  canal  opens  on  the  front  of  the  tooth  ;  this  disposi¬ 
tion  of  parts  has  been  copied  in  the  points  of  syringes  for 
making  subcutaneous  injections. 

(b  Transverse  section  of  tooth-sac  of  poison  fang  of  Viper,  prior  to  the 
complete  closure  of  the  poison  tube  by  the  meeting  together  of  the  two 
cornua  of  the  dentine. 


270 


A  MANUAL  OF  DENTAL  ANATOMY. 


The  dentine  is  continued  down  to  a  very  fine  point,  and 
it  is  cased  by  an  exceedingly  thin  layer  of  enamel,  not 
much  more  than  0f  an  inch  in  thickness  in  our  common 
English  viper :  thus  the  utmost  sharpness  is  secured, 
without  loss  of  elasticity,  which  would  have  ensued  had 
its  point  been  made  up  of  brittle  enamel  only.  Enamel 
covers  the  whole  exterior  of  the  tooth  but  does  not  extend 
into  the  poison  canal  in  the  viperine  snakes ;  in  Hydrophis 


Fig.  113  (J). 


I  believe  that  it  does.  As  the  point  is  simple,  the  tooth 
germ  of  a  poison-fang  only  becomes  distinguishable  from 
that  of  another  ophidian  tooth  after  the  tip  of  the  tooth  has 
been  formed,  when  a  groove  appears  in  its  side  (see  8  and  9, 
in  Fig.  114). 

It  being  the  habit  of  poisonous  snakes  to  make  use  of 
these  weapons  to  kill  their  prey,  which  they  consequently 
do  not  swallow  alive,  it  would  obviously  subject  them  to 
no  little  inconvenience  to  be  without  these  weapons  for 

P)  Transverse  section  of  the  poison  fang  of  a  Rattlesnake,  a.  Pulp- 
cavity.  d.  Dentine. 


THE  TEETH  OF  REPTILES. 


271 


any  considerable  length  of  time,  while  from  their  habit  of 
striking  living  prey  the  long  fangs  must  be  very  liable  to 
being  broken  off  by  the  jumping  away  of  the  creature  struck, 
to  say  nothing  of  the  great  force  with  which  the  blow  is 
given. 

In  the  most  typical  (viperine)  poisonous  snakes  the 
succession  of  teeth  is  conducted  upon  a  plan  which  is 
unique,  and  which  is  excellently  adapted  to  save  loss  of 
time  in  the  replacement  of  a  lost  poison  fang.  Upon  the 
movable  maxillary  bones  there  is  space  enough  for  two 
poison  fangs,  side  by  side;  only  one,  however,  is  fully 
anchylosed  to  the  bone  at  a  time,  and  occupies  a  place  to 
the  extreme  right  or  extreme  left  of  the  bone,  leaving  vacant 
space  for  another  by  its  side. 

When  the  tooth  in  use  falls,  it  will  be  succeeded  by  a 
tooth  upon  the  vacant  spot  by  its  side,  not  upon  the  spot 
upon  which  itself  stood,  so  that  the  places  on  the  right 
and  the  left  of  the  bone  are  occupied  alternately  by  the  tooth 
in  use.  Thus  in  Fig.  Ill,  the  poison-fang  of  the  snake’s 
right  side  is  seen  occupying  a  position  on  the  extreme  out¬ 
side  of  the  maxillary  bone,  while  its  left  poison  fang  is  fixed 
on  the  inside  of  the  maxillary  bone. 

The  upper  boundary  of  Fig.  114  is  formed  by  the  flap 
of  mucous  membrane  which  covers  in  the  poison  fang  when 
at  rest.  Nos.  1  and  2  lie  in  the  pouch  formed  by  it,  the 
section  happening  to  be  taken  from  a  specimen  in  which  the 
tooth  was  about  to  be  changed.  In  most  specimens  one 
tooth  only,  the  tooth  actually  in  use,  is  seen  in  this  position. 

A  flap  hanging  free  across  this  space  serves  apparently  to 
keep  teeth  of  the  one  series  from  getting  over  to  the  other 
side,  and  probably  serves  to  hold  in  place  the  reserve  tooth 
when  the  older  tooth  is  erected  for  biting. 

The  reserve  poison  fangs,  as  many  as  ten  in  number  in 
the  Rattlesnake,  are  likewise  arranged  in  two  parallel  series, 
in  which  the  teeth  exist  in  pairs  of  almost  equal  age ;  the 


272 


A  MANUAL  OF  DENTAL  ANATOMY. 


tooth  in  use  is  thus  derived  alternately  from  the  one  and 
the  other  series,  as  is  indicated  by  the  consecutive  numbers 
in  the  figure,  a  septum  of  connective  tissue  keeping  the  two 
series  of  teeth  distinct  from  one  another. 

The  teeth  being  arranged  in  pairs  of  almost  equal  age, 
suggest  that  the  succession  is  both  rapid  and  regular.  All 


Fig.  114  f1). 


the  reserve  teeth  lie  recumbent  in  and  behind  the  sheath 
of  mucous  membrane  which  covers  in  the  functional  tooth. 

This  arrangement  of  the  successional  teeth  in  a  paired 
series  does  not  exist  in  the  Cobra,  in  which  the  successional 
teeth  form  but  a  single  series ;  perhaps  this  may  serve  to 
explain  the  preference  of  the  snake  charmers  for  the  Cobra, 

O  Transverse  section  of  the  reserve  poison  fangs  of  a  Viper.  1.  Tooth 
at  present  in  use,  in  its  recumbent  position  ;  were  it  erect,  it  would  be 
withdrawn  from  view,  or  else  seen  in  longitudinal  section.  2.  Tooth 
which  will  next  succeed  to  No.  1.  3,  4,  5,  &c.  Tooth-sacs  numbered  in 

the  order  in  which  they  will  succeed. 


THE  TEETH  OF  REPTILES. 


273 


which  would  probably  take  longer  to  replace  a  removed 
poison  fang  than  a  viperine  snake  would  (1). 

But  in  the  colubrine .  venomous  snakes  the  successional 
poison  fang  sometimes  makes  its  way  to  a  spot  a  little  to  the 
side  of  its  predecessor,  so  that  there  may  possibly  be  no  loss 
of  time ;  and  notwithstanding  that  they  are  in  a  measure 
transitional  forms  between  the  harmless  and  the  viperine 
snakes,  some  of  them  are  most  virulently  poisonous  and 
deadly  in  their  bite  (2). 

This  arrangement  of  two  distinct  chains  of  younger 
I  developing  organs,  all  destined  to  keep  the  creature 

I  always  supplied  with  one  organ  in  a  state  of  efficiency,  is, 
so  far  as  I  know,  without  parallel. 

Like  other  ophidian  teeth  the  poison  fangs  become  an- 
chylosed  to  the  bone  which  carries  them,  their  secure 
fixation  being  aided  by  the  base  of  the  tooth  being  fluted,  as 
well  as  by  a  sort  of  buttress  work  of  new  bone  being  thrown 
out  to  secure  each  newr  poison  fang  as  it  comes  into 
place. 

The  poison  is  secreted  by  a  salivary  gland  homologous 
with  the  parotid  ;  by  an  especial  arrangement  of  the  muscles 
and  fascia  about  it  the  erection  of  the  poison  fang  and  the 
infliction  of  the  bite  cause  a  copious  stream  of  poison  to  be 
ejected.  The  duct  terminates  in  a  sort  of  papilla,  close  to 
the  superior  orifice  of  the  tube  in  the  fang ;  the  passage  of 
a  considerable  portion  of  the  poison  down  the  tube  is  secured 

(b  An  inquiry  inserted  in  an  Indian  newspaper  elicited  the  following 
answer: — “I  have  frequently  seen  snake-charmers  exhibit  snakes  of  the 
family  Viperidce,  chiefly  the  Daboia  Russelii  and  Echis  carinata.  I  have 
also  been  told  by  some  snake-charmers  that  they  considered  the  Daboia 
even  more  poisonous  than  the  cobra  ;  and  judging  from  the  cautious  way  in 
which  they  handled  these  snakes — never  lifting  them  off  the  ground  with¬ 
out  first  putting  a  stick  on  their  necks  to  hold  them  down — I  feel  pretty 
sure  tliey  all  consider  the  vipers  more  dangerous  than  the  cobras.” 

(2)  I  have  given  a  more  detailed  account  of  the  succession  of  poison 
fangs  in  the  Philos.  Trans.,  1876,  Part  i. 


274 


A  MANUAL  OF  DENTAL  ANATOMY. 


as  to  possess  sharp  edges ;  but  they  vary  much  in  form  in 
different  species. 

The  teeth  are  lodged  in  distinct  tubular  alveolar  cavities, 
to  the  walls  of  which  they  do  not  become  anchylosed,  and 
they  are  tolerably  constant  in  number  in  the  same  species. 

In  parts  of  the  mouth  certain  teeth  are  developed  to  a 
greater  length  than  those  nearest  to  them ;  thus,  in  the 
Crocodile  proper,  the  first  and  fourth  lower  teeth  are  spe- 

(l)  Jaws  of  the  Crocodile.  The  first,  fourth,  and  eleventh  teeth  in  the 
lower  jaw,  and  the  third  and  ninth  in  the  upper,  are  seen  10  attain  to  a 
larger  size  than  the  others. 


by  the  close  apposition  of  a  shield  of  mucous  membrane, 
which  is  strained  over  the  erected  tooth. 

In  Crocodilia  the  teeth  are  confined  to  the  margins  of 
the  jaws,  where  they  are  very  formidable  in  size  and  sharp¬ 
ness.  The  individual  teeth  are  generally  conical,  sharply 
pointed,  and  often  a  little  compressed  from  side  to  side,  so 

Fig.  115  (l). 


THE  TEETH  OF  REPTILES. 


275 


cially  large,  while  in  the  extinct  African  Galesaurus  the 
difference  is  so  marked  that  both  in  the  upper  and  lower 
jaws  the  teeth  might  be  grouped  as  incisors  and  canines,  so 
far  as  size  and  probable  function  go  in  such  a  classification. 

In  structure  the  teeth  of  crocodiles  consist  of  hard,  fine 
tubed  dentine,  with  an  investing  cap  of  enamel,  and  in  ad- 

Fig.  116  p). 


dition  a  coating  of  cementum  on  their  implanted  portions. 
As  already  mentioned,  they  are  implanted  in  tubular 
sockets ;  new  successional  teeth  are  being  continually  de¬ 
veloped  at  the  inner  side  of  their  bases,  and  as  these  attain 
to  a  certain  size,  absorption  attacks  the  base  of  the  older 
tooth,  and  its  successor  moves  into  the  space  so  gained,  so 
that  it  comes  to  be  situated  vertically  beneath  the  older 
tooth.  Id  its  further  growth  it  causes  yet  more  absorption 

P)  Transverse  section  of  the  lower  jaw  of  a  young  Alligator,  a .  Oral 
epithelium,  b.  Bone  of  socket,  d.  Dentine  of  old  tooth.  2.  Tooth  next 
|  in  order  of  succession,  which  is  causing  absorption  of  one  side  of  the  base 
of  the  older  tooth.  3.  Young  tooth-germ. 


276 


A  MANUAL  OF  DENTAL  ANATOMY. 


of  the  older  tooth,  which  it  ultimately  pushes  out  in  front 
of  it,  sometimes  carrying  the  remains  of  the  old  tooth  like 
a  cap  upon  its  own  apex  when  it  first  emerges.  Each  new 
tooth  vertically  succeeds  its  predecessor ;  hence  no  additional 
teeth  are  added,  but  the  young  newly  hatched  crocodile  has 
as  many  teeth  as  a  full-grown  one. 

In  the  extinct  Ichthyosaurus  the  teeth,  while  forming  an 
armature  not  unlike  that  of  some  of  the  crocodiles,  were 
not  implanted  in  distinct  sockets,  but  were  lodged  in  a 
continuous  shallow  groove,  with  but  slight  indications  of 
transverse  divisions. 

The  huge  Dinosauria,  some  of  which  must  have  been  thirty 
feet  in  length,  had  teeth  implanted  in  imperfect  sockets,  the 
outer  alveolar  wall  being  considerably  higher  than  the  inner, 
and  the  transverse  septa  not  very  complete.  The  roots  of 
the  teeth  were  more  or  less  perfectly  cylindrical,  and  the 
enamelled  crowns  compressed  and  expanded,  with  trenchant 
edges.  The  tooth  of  the  Iguanodon  will  serve  as  a  fair 
example  of  a  Dinosaurian  tooth :  the  crown  is  greatly 
expanded,  and  presents  anterior  and  posterior  sharp  notched 
margins  ;  the  enamel  is  laid  over  the  outer  surface  of  upper 
teeth,  and  the  inner  of  lower  teeth.  The  enamelled  surface 
is  ridged,  so  that  as  it  wears  down  a  notched  edge  is 
maintained.  Moreover  the  maintenance  of  a  sharp  edge  is 
further  secured  by  the  dentine  on  the  enamelled  side  of  the 
crown  being  of  the  hard  unvascular  variety,  that  on  the  inner 
being  vasodentine  and  therefore  softer.  The  remnant  of 
the  pulp  ossifies,  and  comes  into  use,  as  these  teeth  remained 
at  work  until  worn  quite  to  a  flat  surface.  The  root  portion 
was  smooth,  round,  and  curved. 

Professor  Marsh  (American  Journal  of  Science,  March, 
1880)  has  described  and  figured  a  peculiar  Dinosaurian  den¬ 
tition,  in  a  reptile  to  which  he  gives  the  name  of  Stegosaurus ; 
the  teeth  are  slightly  compressed  transversely,  and  are 
covered  with  a  thin  enamel ;  the  roots  are  long  and  slender, 


THE  TEETH  OF  REPTILES. 


277 


implanted  weakly  in  separate  sockets.  But  at  the  inner 
side  of  the  roots  of  the  teeth  in  use  were  no  less  than 
five  successional  teeth,  in  graduated  stages  of  develop¬ 
ment,  ready  to  ultimately  take  its  place ;  so  large  a  number 
of  successional  teeth  has  not  hitherto  been  met  with  in  a 
Dinosaur. 

A  very  remarkable  carnivorous  reptile  as  large  as  a  lion 
has  been  described  by  Professor  Owen  (Quart.  Journal 
Geolog.  Society,  1876,)  under  the  name  of  Cynodraco  major, 
for  the  reception  of  which  he  proposes  a  new  reptilian  order, 
that  of  Theriodontia.  Its  dentition  is  not  completely  known, 
but  it  possessed  in  the  lower  jaw  eight  incisors,  of  which  the 
first  is  the  smallest,  and  a  canine  of  moderate  size.  The 
upper  incisors  are  not  known,  but  there  were  a  pair  of  upper 
canines  of  such  size  that  they  extended  down  along  the 
outside  of  a  flattened  portion  of  the  lower  jaw,  like  the 
canine  teeth  of  Machairodus  and  those  of  Dinoceras.  The 
hinder  margins  of  these  canines  were  trenchant,  and  finely 
serrated. 

This  protection  of  an  especially  long  upper  tooth  by  a 
corresponding  down  growth  of  the  lower  jaw  is  by  no  means 
an  unusual  provision  of  nature.  Besides  being  met  with  in 
the  instances  cited,  it  is  seen  in  Tinoceras,  another  of  the 
Dinocerata,  and  in  Chauliodus,  a  deep-sea  fish  dredged  up 
by  the  “  Challenger.”  It  is,  however,  not  a  universal 
structure,  as  it  is  quite  absent  in  the  musk  deer. 

The  Fterosauria,  or  flying  reptiles,  have,  since  the 
discovery  of  toothed  birds,  become  of  special  interest  to 
the  odontologist.  The  wings  were  stretched  membranes, 
like  those  of  a  bat,  and  the  measurement  across  their  tips 
in  some  of  the  largest  must  have  been  twenty-five  feet ; 
but  most  of  those  known  were  much  smaller,  from  10  to  15 
inches  in  total  length  of  body.  In  the  Pterodactyls  the  jaws 
are  furnished  with  long,  slender,  sharp  teeth  in  their  whole 
length ;  but  in  Bamphorhynchus  the  anterior  extremities  of 


278 


A  MANUAL  OF  DENTAL  ANATOMY. 


the  jaws  are  without  teeth,  and  it  has  been  conjectured  that 
these  portions  were  sheathed  in  horny  beaks. 

And  Prof.  Marsh  (American  Journal  of  Science,  1876,)  has 
discovered,  in  the  same  formation  in  which  he  found  the 
toothed  birds,  several  species  of  Pterodactyls  wholly  without 
teeth,  for  which  the  generic  name  Pteranodon  is  proposed. 

The  jaws,  which  are  more  like  those  of  birds  than  those  of 
any  known  reptile,  show  no  traces  of  teeth,  and  the  pre- 
maxillaries  seem  to  have  been  encased  in  a  horny  covering. 


The  Teeth  of  Birds. 

Prior  to  the  discovery  by  Professor  Marsh  of  Yale  College, 
in  1870,  of  the  remains  of  birds  with  teeth  in  the  cretaceous 
formations  of  Western  Kansas,  little  was  with  certainty 
known  about  the  existence  of  teeth  in  any  bird,  although 
one  or  two  fossils,  leading  to  the  suspicion  that  birds  might 
have  possessed  teeth,  were  known.  The  state  of  knowledge 
up  to  that  time  has  been  clearly  summarised  by  Mr.  Wood¬ 
ward  (Popular  Science  Keview,  1875,)  to  this  effect  :  that 
it  had  been  long  supposed  that  no  examples  of  teeth  were  to 
be  met  with  amongst  the  birds,  although  some,  such  as  the 
Merganser,  have  the  margins  of  the  bill  serrated,  so  that  the 
functions  of  teeth  are  discharged  by  this  horny  armature  of 
the  jaws. 

It  is  noteworthy  that  the  margin  of  the  bone  of  the  jaws 
is  also  serrated,  each  serration  corresponding  to  a  similar 
serration  in  the  bill.  In  the  fossil  bird  described  by  Pro¬ 
fessor  Owen,  from  the  London  clay,  under  the  name  of 
Odontopteryx  toliapicus,  the  form  of  the  bill  is  not  known, 
but  the  margins  of  the  jaws  are  furnished  with  strong  bony 
prominences,  far  more  conspicuous  than  those  of  the 
Merganser.  And  Geoffroy  St.  Hilaire  had  described  a  series 
of  vascular  pulps  as  existing  on  the  margin  of  the  jaw  of 


THE  TEETH  OF  BIRDS . 


279 


parroquets  just  about  to  be  hatched,  which,  though  destined 
to  form  a  horny  bill,  and  not  to  be  calcified  into  teeth, 
yet  strikingly  recal  dental  pulps.  Then  there  is  also  the 
famous  fossil  Archaeopteryx,  an  anomalous  oolitic  bird,  with 
a  long  and  jointed  tail,  which  is  by  many  zoologists  believed 
to  have  possessed  teeth.  There  is  a  flaw  in  the  evidence, 
however,  inasmuch  as  the  toothed  jaw  is  not  in  situ ,  and 
therefore  may  possibly  have  belonged  to  some  other  animal 
than  that  perpetuated  in  the  rest  of  the  fossil  impression, 
though  probability  is  altogether  in  favour  of  its  really 
belonging  to  the  Archaeopteryx. 

In  successive  expeditions,  conducted  under  great  difficulties 
owing  to  the  extremes  of  heat  and  cold,  and  to  the  hostility 
of  the  Indians,  the  remains  of  no  less  than  one  hundred 
and  fifty  different  individuals  referable  to  the  sub-class 
Odontornithes  have  been  obtained  by  Prof.  Marsh  ;  they 
are  classified  under  nine  genera,  and  twenty  species. 

They  are  referable  to  two  widely  different  types,  one 
group  consisting  of  comparatively  small  birds,  with  great 
power  of  flight,  and  having  their  teeth  implanted  in  distinct 
sockets  (Odontotornse,  illustrated  by  the  genus  Ichthyornis 
as  a  type) ;  the  other  group  consisting  of  very  large  swimming 
birds,  without  wings,  and  having  teeth  in  grooves  (Odontolcse, 
type  genus  Hesperornis). 

In  Ichthyornis  the  teeth  were  about  twenty-one  in  number 
in  each  ramus,  all  sharp  and  pointed,  and  recurved  ;  the 
crowns  were  coated  with  enamel,  and  the  front  and  back 
edges  sharp  but  not  serrated. 

They  are  implanted  in  distinct  though  shallow  sockets, 
and  the  maxillary  teeth  are  a  little  larger  than  those 
opposing  them ;  the  pre-maxillaries  were  probably  edentulous, 
and  perhaps  covered  with  a  horny  bill. 

In  the  lower  jaw  the  largest  teeth  occur  about  the  middle 
of  the  ramus,  those  at  its  posterior  end  being  materially 
smaller ;  and  the  sockets  are  deeper  and  stronger  than  in  the 


280 


A  MANUAL  OF  DENTAL  ANATOMY. 


Fig.  117  0). 
ii  MS. 
A 


I 


upper  jaw.  The  succession  takes  place  vertically,  as  in 
Crocodiles  and  Dinosaurs. 

The  genus  Hesperornis,  probably 
diving  birds,  includes  species  6  feet  in 
length  :  as  has  already  been  mentioned 
the  teeth  are  not  implanted  in  distinct 
sockets,  but  lie  in  a  continuous  groove 
like  those  of  Ichthyosaurus ;  slight 
projections  from  the  lateral  walls  indi¬ 
cate  a  partitioning  off  into  sockets, 
but  nothing  more  than  this  is  attained, 
and  after  the  perishing  of  the  soft  parts 
the  teeth  were  easily  displaced,  and  had 
often  fallen  out  of  the  jaws.  The  pre¬ 
maxillary  is  edentulous,  but  the  teeth 
extend  quite  to  the  anterior  extremity 
of  the  lower  jaw :  in  one  specimen 
there  are  fourteen  sockets  in  the  max¬ 
illary  bone,  and  thirty-three  in  the 
corresponding  lower  ramus. 

The  successional  tooth  germs  were 
formed  at  the  side  of  the  base  of  the 
old  ones,  and  causing  absorption  of  the 
old  roots,  migrated  into  the  excavations 
so  formed,  grew  large,  and  ultimately 
expelled  their  predecessors,  as  is  seen  in 
the  accompanying  figure. 

In  structure  these  teeth  consist  of 
hard  dentine,  invested  with  a  rather  thin  layer  of  enamel, 
and  having  a  large  axial  pulp  cavity.  The  basal  portion 
of  the  roots  consists  of  osteodentine. 

The  outer  side  of  the  crown  is  nearly  flat,  the  inner  strongly 


0)  Mandible  of  Ichtliyornis  (after  Prof.  Marsh).  A.  Side  view,  show¬ 
ing  the  teeth  in  situ.  B.  View  of  upper  surface,  showing  the  sockets  in 
which  the  teeth  were  implanted. 


THE  TEETH  OF  BIRDS. 


281 


convex  :  the  junction  of  these  surfaces  is  marked  by  a  sharp 
ridge,  not  serrated. 

In  form  the  teeth  of  Hesperornis  present  a  close  resem- 
blanceto  those  of  Mosasaurus,  a  great  extinct  lizard. 

Indeed,  as  Prof.  Marsh  observes,  “  in  all  their  main 
features  the  teeth  of  Hesperornis  are  essentially  reptilian 


Fig.  118  (l). 

A  B 


and  no  anatomist  would  hesitate  to  refer  them  to  that  class, 
had  they  been  found  alone.  Combined  with  the  other 
reptilian  characters  of  Hesperornis  ....  they  clearly 
indicate  a  genetic  connection  with  that  group.  ” 

In  the  dentine  contour  lines  are  abundant ;  the  enamel 
is  so  dense  as  to  appear  structureless,  and  there  is  no  coronal 
cementum. 

The  foregoing  account  is  condensed  from  the  magnificent 
volume  published  by  the  United  States  Government  Geo¬ 
logical  Exploration.  (Odontornithes,  a  monograph,  &c.,  by 
0.  C.  Marsh,  Prof,  of  Palaeontology,  Yale  College.) 

With  these  notable  exceptions,  the  jaws  of  all  known  birds 
are  toothless,  the  horny  cases  forming  their  beaks  taking  the 
places  and  fulfilling  the  functions  of  teeth. 

f1)  (After  Prof.  Marsh. )  A.  Hesperornis  regalis,  with  successional  tooth 
in  an  excavation  at  its  base ;  enlarged  eight  diameters.  B.  Tooth  of 
Mosasaurus  princeps,  half  natural  size. 


282 


A  MANUAL  OF  DENTAL  ANATOMY. 


The  evidence  that  true  teeth  may  become  replaced  by 
horny  teeth,  these  again  coalescing  with  their  neighbours  to 
form  a  horny  casing,  has  been  given  at  page  44. 

It  would  therefore  seem  possible  that  the  ancestral  birds 
all  had  true  teeth,  and  it  is  possible  that  a  sufficiently  ex¬ 
tended  search  might  reveal  rudimentary  teeth  surviving 
beneath  the  functional  horny  bill,  or  even  possibly  above  it, 
like  those  of  Ornithorhynchus. 


CHAPTER  VIII. 


THE  TEETH  OF  MAMMALIA. 

The  mammalia  are  usually  now  divided  into  three  groups 
— Frototheria,  Metatheria,  and  Eutheria. 

The  Frototheria  comprise  but  few  animals  numerically, 
as  no  extinct  forms  are  known,  and  of  living  animals  only  two 
families  exist,  namely,  the  Ornithorhyncidse  and  the  Echidnidse. 

They  stand  at  the  bottom  of  the  mammalian  class,  and 
present  many  points  of  affinity  with  lower  vertebrates, 
particularly  with  Sauropsida  and  Batrachia. 

Recent  discoveries  have  added  fresh  interest  to  at  all 
events  the  Ornithorhynchus,  which  has  been  found  to  lay 
eggs,  and  to  be  possessed  of  a  unique  arrangement  of  teeth. 

Metatheria,  like  the  preceding  group,  have  characters 
which  place  them  low  in  the  mammalian  scale,  but  they  are 
numerously  represented  at  the  present  day,  comprising  the 
animals  known  as  Marsupials,  which  practically  monopolize 
the  Australian  region,  and  exist  also  in  the  American  con¬ 
tinent.  In  former  times  they  existed  over  other  portions  of 
the  globe,  and  the  earliest  mammalian  fossils  are  perhaps 
referable  to  the  group. 

Eutheria  comprise  all  the  mammals  in  whom  the  young 
are  nourished  by  means  of  a  placenta. 

It  must  not  be  supposed  by  the  student  that  the  Metatheria 
of  the  present  day  are  descended  directly  from  the  Frototheria , 
or  that  the  Eutheria  are  direct  descendants  of  the  marsu¬ 
pials  ;  it  is  more  probable  that  exceedingly  early  and  quite 
unknown  mammalian  forms  have  given  rise  to  each  of  these 


284 


A  MANUAL  OF  DENTAL  ANATOMY. 


the  marsupials  a  good  deal,  giving  rise  to  a  large  number  of 
forms,  but  that  the  Eutheria  have  far  outstripped  the  others, 
and  have  been  and  are  supplanting  them  in  all  directions. 

It  will  be  more  convenient  in  this  book  to  postpone  the 
consideration  of  the  marsupials  till  after  the  dentitions  of 
placental  mammals  have  been  described. 


Prototheria. 

The  Echidna  is,  so  far  as  is  known,  entirely  edentulous. 

The  Ornithorhynchus,  which  in  its  soft  parts  and  skeleton 
alike  differs  from  higher  mammals  in  points  which  approach 
the  characters  of  Sauropsida,  is  furnished  with  wide  flattened 
jaws  in  which  horny  plates  fulfil  the  function  of  true  teeth; 
from  this  peculiarity  comes  its  name  of  duck-billed  platypus. 

Recently  Mr.  Caldwell  discovered  that  it,  though  possessed 
of  functional  mammary  glands,  lays  eggs,  and  more  recently 
still  Mr.  Poulton  found  that  at  an  early  stage  tooth  germs 
were  present,  as  he  supposed,  underneath  the  horny  plates. 
Following  upon  this  Mr.  Oldfield  Thomas  found  that  its  true 
teeth  came  into  actual  use,  and  that  they  were  not  beneath, 
but  above  the  horny  plates. 

To  take  first  the  dentition,  if  such  it  can  be  called,  of  the  adult 
animals  ;  the  horny  plates  with  which  the  jaws  are  ultimately 
furnished  are  four  in  number  in  each  jaw,  the  anterior  plate 
being  a  thin  long  band  with  a  longitudinal  ridge  and  a 
furrow  in  its  inner  side,  and  the  posterior  plate  a  flat  broad- 
topped  mass  the  surface  of  which  is  roughened  by  a  series  of 
ridges  separated  from  one  another  by  concavities,  the  ridges 
of  the  opposing  plates  interdigitating  with  one  another. 

These  plates  are  simply  pronounced  thickenings  and 
hardenings  of  the  oral  epithelium,  and  their  under-surfaces 
are  penetrated  by  long  papillae,  each  of  which  sends  up  a 
stems,  and  that  the  Prototheria  have  advanced  but  little, 


THE  TEETH  OF  MAMMALIA. 


285 


prolongation  of  soft,  deeply-staining,  cells  from  its  apex.  The 
plates  are  at  their  sides  quite  continuous  with  the  stratum  cor- 
neum  of  the  epithelium,  of  which  their  harder  portions  are  com¬ 
posed  ;  there  is  no  calcification,  and  no  bonystructure  in  them. 
Somewhat  similar  horny  structures  occur  upon  their  tongues. 


Fig.  HOC1). 


A  full  account  of  the  structure  and  form  of  these  plates 
will  be  found  in  a  paper  by  Mr.  Poulton  (  “Quart.  Journ. 
Microscop.  Science,”  Vol.  XXIX.,  n.s.),  which  is  devoted  to  a 
full  description  of  his  most  interesting  and  significant 

(l)  Upper  and  lower  jaws  of  Ornithorhynchus.  From  the  lower  jaw  the 
skin,  &c. ,  has  been  removed,  but  it  remains  upon  the  upper,  a.  Anteiioi 
horny  plate,  b.  Posterior  horny  plate,  with  remains  of  tooth  sockets,  1,  2,  3. 


2S6 


A  MANUAL  OF  DENTAL  ANATOMY. 


discovery  of  the  existence  of  the  true  tooth-germs  which  he 
believed  to  underlie  the  forming  horny  plates. 

From  the  want  of  material  he  was  somewhat  uncertain  as 
to  the  extent  to  which  the  calcification  of  these  teeth  goes, 
and  what  afterwards  becomes  of  them,  but  he  saw  that  there 
were  the  germs  of  four  teeth  in  the  upper,  on  each  side,  and 
probably  the  same  number  in  the  lower,  jaw ;  and  they 
occupy  a  widely  open  furrow,  which  he  thought  was  sub¬ 
sequently  occupied  by  the  horny  plate. 

In  this  connection  it  is  interesting  to  note  that  Professor  • 
Huxley,  in  writing  of  the  Monotremes,  had  years  ago  expressed 
the  conviction  that  there  is  good  reason  to  suppose  that 
edentulous  forms  are  modified  descendants  of  toothed  forms. 

Mr.  Oldfield  Thomas  and  Prof.  Stewart  subsequently 
found  that  the  true  teeth  of  Ornithorhynchus  are  cut,  and  for 
a  time  are  in  actual  use  ;  they  are  twelve  in  number,  two  on 
each  side  being  of  some  size,  and  the  third  very  small.  The 
upper  teeth  have  broad-topped  crowns,  with  two  long  cusps 
on  the  inner  edge,  and  a  crenated  border  along  the  outer 
edge  with  many  small  cusps  ;  in  the  lower  this  is  reversed. 
They  have  low  broad  crowns  with  short  stunted  roots,  by 
which,  however,  they  are  for  a  time  pretty  firmly  held. 
Instead  of  being  beneath  the  horny  plates  they  are  on  the 
top  of  them,  and  their  implantation  is  peculiar ;  the 
expanded  crowns  narrow  rapidly  at  the  neck,  and  they  are 
surrounded  by  a  very  dense  and  thick  epithelium,  almost 
horny,  which  rises  into  a  ring  round  them  and  dips  under¬ 
neath  the  expanded  portion,  so  that  the  crown  lies  in  a  sort 
of  cap  of  horny  consistency. 

This  cup  is  not  complete  at  the  bottom,  but  the  roots 
pass  through  it  and  fit  depressions  in  the  bone,  which  is 
perforated  by  foramina  for  their  vessels  and  nerves.  When 
the  creature  is  about  twelve  inches  long  the  teeth  are  shed, 
and  then  the  horny  cups  grow  in  underneath  and  become 
complete  ;  thus  the  curiously  cupped  and  sculptured  surface 


THE  TEETH  OF  MAMMALIA. 


287 


of  the  homy  plates  which  have  been  so  long  familiar  has  its 
form  determined  by  once  having  formed  the  bed  for  a  tooth 
with  several  roots,  and  although  the  horn  grows  underneath 
and  fills  up  the  holes  for  the  roots  to  go  through,  yet  the  old 
general  form  is  maintained  by  the  horny  plate  which  serves 
as  the  organ  of  mastication  throughout  the  life  of  the  animal. 


Fig.  120  0). 


Fig.  121  (2). 


So  far  as  is  known  this  is  an  arrangement  quite  unique 
amongst  mammals,  or  indeed  any  other  tooth-bearing 
creatures. 

The  horny  plates  are  therefore  not  at  all  to  be  regarded 
as  horny  teeth,  but  they  are  epithelial  structures  which 

0)  Horny  plate,  a,  of  a  half-grown  Ornithorhynchus,  with  empty  pits ; 
b,  for  the  reception  of  the  teeth. 

(2)  Horny  plate  with  teeth  in  situ.  c.  Long  cusp  of  tooth,  after  Prof. 
Stewart,  from  a  specimen  in  the  Royal  College  of  Surgeons’  Museum. 


288 


A  MANUAL  OF  DENTAL  ANATOMY. 


take  the  place  of  the  teeth  after  these  are  shed,  and  there¬ 
fore  they  are  not  closely  homologous  with  the  horny  teeth  of 
lampreys  and  myxinoids. 

The  true  teeth  consist  of  a  body  of  dentine,  with  a  central 
pulp  cavity,  capped  with  thin  but  hard  enamel,  and  implanted 
by  short  roots,  the  breadth  of  crown  greatly  exceeding  its 
vertical  dimension. 

The  enamel  is  apparently  of  simple  structure,  and  the 
dentine  is  permeated  by  fine  dentinal  tubes  and  beset  with 
a  wonderful  number  of  interglobular  spaces,  which  in  parts 
of  the  crown  mask  its  tubular  structure.  In  the  principal 
cusp  larger,  apparently  vascular,  canals  exist,  and  as  one 
approaches  the  stunted  roots,  a  somewThat  abrupt  transition 
in  structure  takes  place,  all  dentinal  tubes  disappearing,  and 
large  lacunae  appearing. 

The  roots  are  hence  of  softer,  coarser  material  than  the 
crown,  which  itself  is  not  of  a  high  type  of  dentine  structure. 


Fig.  122  (J). 


Thus  the  dentine  structure  of  the  tooth  is  somewhat  that 
which  we  are  accustomed  to  see  as  a  result  of  pathological 
processes,  and  would  suggest,  so  far  as  it  goes,  that  the 
Ornithorhynchus  tooth  has  degenerated  from  some  earlier 
and  more  complete  tooth-form  in  which  the  roots  were 
properly  developed. 

I  am  not  acquainted  with  any  example  of  this  degeneration 
in  the  type  of  dentine  formation  as  the  root  portion  of  the 
tooth  is  approached  in  any  mammalian  tooth :  in  those  teeth 


(b  Molar  tootli  of  Ornitliorhynchus.  c.  Long  cusp. 


THE  TEETH  OF  MAMMALIA. 


289 


which  have  no  roots,  if  such  an  expression  may  be  allowed, 
but  which  are  about  to  become  anehylosed  to  the  bone, 
something  of  the  kind  may  be  seen  (cf.  also  the  tooth  of 
Hesperornis,  p.  280). 

The  British  Museum  specimen  described  by  Mr.  Oldfield 
Thomas  (Proc.  Boy.  Soc.,  May,  1889),  show  that  the  teeth 
were  subjected  to  severe  attrition,  as  one  which  was  about 
to  be  shed  was  worn  as  thin  as  paper.  No  tooth,  fossil  or 
recent,  corresponds  in  naked-eye  characters  with  that  of 
Ornithorhynchus,  though  that  of  the  mesozoic  Microlestes 
does  so  in  some  degree,  so  that  Mr.  Oldfield  Thomas  gives  a 
figure  of  it  for  comparison. 

Microlestes  has  generally  been  looked  upon  as  a  mar 
supial,  allied  to  Plagiaulax,  and  Prof.  Cope  has  suggested 
that  all  the  group  of  multituberculate  toothed  mesozoic 
mammals  may  have  been  monotremes. 

But  a  microscopic  examination  of  a  tooth  of  Microlestes, 
which  Mr.  Poulton  kindly  allowed  me  to  make,  shows  no 
close  resemblance  to  the  recent  marsupials,  for  the  ename 
is  not  clearly  penetrated  by  dentinal  tubes,  nor  does  it  pre¬ 
sent  the  peculiarities  of  structure  found  in  Ornithorhynchus 
Thus  its  structure  gives  no  help,  but  rather  goes  to  render 
still  more  indefinite  its  probable  zoological  position. 

But  although  these  discoveries  seem  to  carry  us  back  to  a 
form  of  mammalian  tooth  very  remote  in  point  of  time,  it  has 
yet  by  no  means  a  simple  crown,  and  we  are  still  very  far  from 
knowing  anything  which  can  be  regarded  as  a  primitive  parent 
form  whence  all  mammalian  teeth  may  have  been  derived. 

Still  the  discovery  is  of  incalculable  value,  inasmuch  as 
many  of  the  early  mammalia  are  known  to  us  only  by  teeth, 
and  the  form  and  structure  of  a  monotrematous  tooth  gives 
us  something  far  lower  in  the  evolutionary  scale  than  had 
hitherto  been  known. 

The  Echidna,  or  scaly  Ant-Eater,  also  an  Australian  mam¬ 
mal,  has  no  teeth  whatever,  so  far  as  is  at  present  known. 


290 


A  MANUAL  OF  DENTAL  ANATOMY . 


EUTHERIA. 

There  is  great  difficulty  in  arranging  Placental  Mammals 
in  any  order  of  sequence,  inasmuch  as  those  now  existing, 
and  those  fossil  forms  known  to  us,  form  but  a  small  fraction 
of  all  which  have  once  existed.  And  although  no  modem 
naturalist  can  well  doubt  that  all  existing  mammals  are 
lineal  descendants  of  a  smaller  number  of  forms  previously 
existing,  yet  they  do  not  admit  of  being  arranged  on  any  one 
stem,  and  are  not  at  all  lineal  descendants  of  one  another. 

Prof.  Flower  (art.  Mammalia,  Encyclop.  Britannica)  places 
them  provisionally,  and  for  want  of  a  better  arrangement, 
thus : — 

Edentata — Sloths,  Ant-Eaters,  Armadillos,  &c. 

Sirenia — So-called  Herbivorous  Cetacea,  Manatee,  Dugong,  &c. 
Cetacea — Sperm  Whales,  Porpoises,  Whalebone  Whales,  Sec. 
Insectivora — Hedgehogs,  Moles,  &c.,  Sec. 

Chiroptera — Bats. 

j Rodentia  — Hares,  Rabbits,  Rats,  &c. 

Ungvlata  (Hoofed  Mammals) — 

Hyrax — The  single  family  Hyracoidea. 

Prohoscidea — Dinotheriums,  Mastodons,  Elephants. 

AmMypoda — Great  extinct  animals  from  American  Eocene  forma¬ 
tions,  Dinoceras,  &c. 

JJngulata  vera — Perissodactyle  Ungulates,  Horse  Tapir,  Rhino¬ 
ceros,  &c. 

Artiodactyle  Ungulates,  Pigs,  Camels,  Ruminants, 
Sec. 

Tillodontia — A  group  of  animals  described  by  Profs.  Marsh  and  Cope 
from  American  Eocene,  with  affinities  to  several 
groups,  i.e.  to  Rodents  and  Carnivora,  as  well  as 
to  Ungulates. 

Carnivora  vera — Cats,  Dogs,  Bears,  &c. 

Carnivora,  pinnipedia — Seals,  Walrus,  Sec. 

Primates — Man,  Monkeys,  and  Lemurs. 


INTRODUCTORY  REMARKS. 

It  was  formerly  customary  to  explain  the  various  facts 
which  were  revealed  by  the  study  of  comparative  anatomy 


THE  TEETH  OF  MAMMALIA. 


291 


upon  the  supposition  that  there  was  some  sort  of  type  or 
standard  organization,  and  that  all  others  wrere  arrived  at 
by  modifications  and  departures  from  this  type,  these 
modifications  being  introduced  with  a  direct  purpose  in 
view,  in  order  to  fit  the  creature  to  a  special  habit  of  life. 

Among  the  matters  which  this  “  type  ”  theory  sought  to 
account  for  was  this  :  when  an  animal  possesses  some  pecu¬ 
liar  organ,  it  is  found  on  close  examination  that  it,  however 
specialised,  is  after  all  only  something  which  allied  animals 
also  possess,  only  it  has  been  exaggerated  or  developed  in  an 
unusual  manner  and  degree  ;  or,  on  the  other  hand,  that 
when  an  organ  is  wanting,  the  suppressed  organ  is  not 
absolutely  abolished,  but  is  to  be  found  stunted  and  in  a 
rudimentary  condition,  instead  of  in  its  ordinary  size  and 
functional  activity. 

This  is  as  true  of  teeth  as  of  any  other  organs ;  indeed 
they  afford  many  admirable  examples  of  the  law. 

Thus  the  tusks  of  the  boar  or  of  the  Sus  babirussa,  large 
and  peculiar  though  they  be,  are  not  new  developments,  but 
are  merely  the  canine  teeth  which  in  these  species  attain  to 
unusual  dimensions.  In  the  same  way  the  enormous 
straight  tusk  of  the  Narwal  (see  p.  343)  is  nothing  more 
than  an  incisor  tooth  of  one  side,  the  fellow  to  which  has 
been  checked  in  its  development ;  but  this  is  not  missing,  for 
it  remains  throughout  the  life  of  the  animal  buried  within 
its  socket.  In  the  female  Narwal  both  of  the  teeth,  being 
rudimentary,  are  permanently  enclosed  within  the  sockets, 
and  are  of  course  not  of  the  smallest  service  to  the  animal, 
directly  or  indirectly ;  furthermore,  as  has  been  shown  by 
Professor  Sir  W.  Turner,  in  young  specimens,  a  second  pair 
of  rudimentary  aborted  incisors  are  to  be  found,  which  in 
the  adults  have  disappeared. 

The  modern  school  of  biologists,  rejecting  the  “arche¬ 
type  ”  theory  refer  these  resemblances  detected  between 
dentitions  upon  the  whole  dissimilar  to  one  another  to  a 


292 


A  MANUAL  OF  DENTAL  ANATOMY. 


more  intelligible  cause,  namely,  inheritance.  Assuming,  as 
the  balance  of  evidence  compels  us  to  assume,  that  the 
many  divergent  forms  which  we  observe  have  been  derived 
by  progressive  modifications  and  differentiations  from  fewer 
ancestral  forms,  we  shall  have  no  difficulty  in  seeing  how, 
by  such  processes  as  we  full  well  know  to  occur,  namely, 
the  dwindling  of  disused  organs  and  the  exaggerated 
development  of  those  very  useful,  great  differences  may 
ultimately  result. 

To  illustrate  what  is  meant  by  this  so-called  “adaptive  modi¬ 
fication,”  this  suppression  of  things  that  are  not  needed,  and 
increased  development  of  those  most  used,  we  may  recur  to  the 
dentitions  of  non-venomous  and  venomous  snakes. 

In  these  we  saw,  in  the  non-venomous  snakes,  the  max¬ 
illary  bones  covered  by  a  row  of  teeth  sub-equal  in  size  ;  then 
in  the  ‘  Colubrine  ’  poisonous  snakes  the  front  tooth  of  the 
row  standing  upon  the  maxillary  bone  having  taken  upon 
itself  a  special  and  important  office,  namely,  the  conveyance 
into  a  wound  of  a  poisonous  saliva ;  coincidently  with  this 
tooth  having  attained  its  increased  size  and  importance,  the 
teeth  behind  it  on  the  maxillary  bone  were  reduced  both  in 
number  and  in  size.  Going  a  step  further,  to  the  Viperine 
poisonous  snakes,  the  now  useless  small  maxillary  teeth 
have  all  disappeared,  leaving  the  poison  fang  alone,  of 
vastly  increased  dimensions,  to  occupy  the  whole  bone. 

But  in  many  poisonous  colubrine  snakes  the  three  or  four 
small  and  useless  teeth  lingering  upon  the  maxillary  bone, 
though  their  function  was  gone,  served  to  indicate  to  us 
in  some  measure  the  gradual  process  by  which  that  singu¬ 
larly  perfect  adaptation  of  means  to  an  end,  the  poison 
apparatus  of  the  viper,  was  arrived  at. 

Mr.  Darwin  has  proved  that  any  modification  in  the 
structure  of  a  plant  or  an  animal,  which  is  of  benefit  to  its 
possessor,  is  capable,  nay,  is  sure,  of  being  transmitted  and 
intensified  in  successive  generations,  until  great  and  material 


THE  TEETH  OF  MAMMALIA. 


293 


differences  have  more  or  less  masked  the  resemblance  to  the 
parent  form. 

Just  as  man,  by  favouring  the  breeding  of  those  modifica¬ 
tions  of  form,  &c.,  that  please  him  best,  has  been  able,  in 
the  course  of  a  few  years — in  a  length  of  time  altogether 
infinitesimal,  as  compared  with  the  time  during  which  the 
surface  of  land  and  sea  has  been  of  pretty  nearly  its  present 
form,  to  say  nothing  of  the  enormously  longer  earlier  geo¬ 
logical  epochs — to  profoundly  modify  the  breeds  of  dogs,  of 
horses,  and  of  numbers  of  plants,  all  of  which  are  absolutely 
known  to  have  had  a  common  origin,  so  in  nature  forces  are 
and  ever  have  been  in  perpetual  operation,  which  effect  the 
same  thing. 

A  pigeon-fancier  wants  a  pigeon  of  particular  plumage, 
with  a  few  feathers  a  little  different  from  any  pigeon  he  has 
ever  seen  or  heard  of  (*) ;  he  knows  by  experience  that  little 
variations  are  for  ever  arising,  and  that  by  watching  a 
sufficient  number  of  young  ones,  and  rigorously  picking  out 
those  which  at  all  tend  in  the  direction  of  what  he  wants, 
he  will  get  what  he  wants,  and  will  even  tell  you  with  confi¬ 
dence  that  in  so  many  years  he  will  make  a  breed  with  the 
peculiarity  desired.  And  exactly  as  the  plumage  that  was 
wanted  is  got,  so  in  nature  the  tooth  that  is  “wanted,” 
i.e.,  the  dentition  that  is  excellently  well  adapted  to  do  its 
work,  by  the  operation  of  that  law  known  as  “  survival  of 
the  fittest  ”  may  have  been  elaborated. 

It  is  quite  enough  that  one  of  the  small  variations  for 
ever  arising  in  animals  shall  be  of  advantage  to  it,  for  us  to 
see  how  the  peculiarity  is  likely  to  be  transmitted  and 
intensified  in  successive  generations. 

The  question  has  been  well  presented  by  Mr.  Wallace, 
who  points  out  that  we  must  not  think  so  much  of  varia¬ 
tions  in  individuals  as  in  groups  of  individuals  :  for  instance, 

f1)  An  eminent  pigeon-fancier,  Sir  J.  Sebright,  told  Mr.  Darwin  that  he 
could  produce  any  given  feather  in  three  years. 


294 


A  MANUAL  OF  DENTAL  ANATOMY. 


it  is  a  familiar  fact  that  people  vary  in  height,  so  that  any 
hundred  persons  may  be  divided  into  fifty  taller  and  fifty 
shorter  persons.  Now  if  a  little  extra  height  were  of  advantage, 
many  or  most  of  the  fifty  would  experience  it,  though  some 
might  not.  In  the  same  way,  if  we  grouped  one  hundred 
animals  whose  teeth  varied  a  little  in  respect  of  strength  into 
the  fifty  weaker  and  the  fifty  stronger,  it  is  easy  to  see  that 
the  stronger  fifty  would  get  the  better  of  the  others  in  the 
struggle  for  existence  on  the  whole,  and  would  be  more 
certain  to  propagate  their  kind,  and  would  repeat  in  a 
majority  of  their  progeny  those  peculiarities  which  had 
helped  themselves  to  live. 

Thus  the  doctrine  of  natural  selection  or  survival  of  the 
fittest,  is  as  fully  applicable  to  the  teeth  of  an  animal  as  to 
any  part  of  its  organisation,  and  the  operation  of  this  natural 
law  will  be  constantly  tending  to  produce  advantageous  or 
“  adaptive  ”  differences.  On  the  other  hand,  the  strong 
power  of  inheritance  is  tending  to  preserve  even  that  which 
in  the  altering  conditions  of  life  has  become  of  very  little 
use,  and  thus  rudimentary  teeth  we  may  understand  to  be 
teeth  which  are  in  process  of  disappearance,  having  ceased 
to  be  useful  to  their  possessors,  but  which  are  still  for  a  long 
time  lingering  upon  the  scene.  It  was  formerly  supposed 
that  the  variations  seized  upon  by  natural  selection  and 
intensified  in  successive  generations  were  of  necessity  small, 
so  small  that  it  was  difficult  to  see  how  their  advantage 
would  really  be  felt. 

But  since  attention  has  been  drawn  to  this  subject, 
and  careful  measurements  and  weighings  have  been  taken 
of  large  numbers  of  wild  specimens  of  the  same  species,  it 
has  been  found  that  the  variations  are  often  far  from  being 
insignificant  in  extent. 

Then  Mr.  Wallace  (Darwinism,  1889)  points  out  that  the 
variation  in  common  species  reaches  often  20  per  cent,  of  the 
size  of  the  part  implicated,  and  this  without  reference  to  the 


THE  TEETH  OF  MAMMALIA.  2? 5 


general  size  of  the  animal.  As  an  example  may  be  taken 
the  jaws  of  the  wolf,  which  in  ten  specimens  varied  to  the 
extent  of  an  inch  and  a  half  in  length.  If  there  be  an 
advantage,  it  is  easy  to  see  how  in  a  few  generations  a  very 
distinct  advance  in  the  direction  of  length  or  shortness  of 
jaw  might  be  established.  ,  \ 

Good  examples  of  rudimentary  teeth  are  to  be  found  in 
the  larval  teeth  of  the  edentulous  sturgeon,  or  of  the 
whalebone  whales,  or  in  the  teeth  buried  beneath  the  horny 
plates  of  the  deflected  portion  of  the  Dugong’s  jaw,  all  of 
these  being  of  absolutely  no  service*  to  their  possessors. 
Some  teeth  have  disappeared  utterly  ;  thus  the  upper 
incisors  of  Ruminants  are  gone,  and  no  rudiments  exist  at 
any  stage  (*)  ;  others  still  remain  in  a  stunted  and  dwindled 
form,  and  do  not  persist  throughout  the  life-time  of  the 
animal,  as  for  instance  the  first  premolars  of  a  horse,  or 
I  two  out  of  the  four  premolars  of  most  bears. 

The  teeth  of  Ornithorhynchus  do  work  for  their  possessor 
till  it  approaches  its  adult  size  :  then  they  are  curiously 
supplanted  by  a  horny  development  of  the  gums. 

It  must  be  borne  in  mind  also  that  variability  downwards 
will  operate  to  slowly  destroy  an  organ  which  is  not  being 
preserved  by  the  action  of  natural  selection. 

Before  leaving  this  section  of  our  subject,  an  instructive 
illustration  of  the  operation  of  these  agencies  may  be  given 

It  is  very  easy  for  us  to  see  how  a  “  rodent  ”  type  of 
dentition  is  beneficial  to  its  possessor  by  rendering  acces¬ 
sible  articles  of  food  whollv  unavailable  for  creatures  which 
have  no  means  of  gnawing  through  a  shell  or  other  hard 
body.  Now  it  happens  that  in  three  regions  of  the  world, 
pretty  completely  cut  off  from  one  another,  three  animals, 
in  parentage  widely  dissimilar,  have  arrived  at  dentitions  of 
“  functionally  rodent  ”  type. 

(b  Statements  to  the  contrary  have  been  made,  and  copied  from  book  to 
book  without  verification. 


296 


A  MANUAL  OF  DENTAL  ANATOMY. 


Thus  in  Australia,  a  region  practically  wholly  monopo¬ 
lised  by  Marsupials,  a  marsupial,  the  Wombat,  has  a  den¬ 
tition  very  much  like  an  ordinary  placental  Rodent.  In  the 
island  of  Madagascar,  one  of  the  very  few  parts  of  the  globe 
without  indigenous  rodents  (except  a  few  Muridte),  a  Lemur- 
ine  animal,  the  Cheiromys,  has  a  dentition  modified  in  a 


Fig.  123  0). 


similar  direction,  (though  it  is  probably  employed  to  get  at  a 
different  sort  of  food) ;  and  elsewhere,  scattered  all  over  the 
world,  we  have  the  ordinary  Rodents. 

In  fact,  three  sets  of  creatures,  as  widely  different  from 
each  other  in  parentage  as  they  well  could  be,  have  been 
modified  by  natural  selection  until  they  have  dentitions,  not 
identical,  but  for  practical  purposes  not  unlike. 

It  is  impossible  to  conceive  that  these  three  creatures 
have  had  anything  in  the  way  of  common  origin  :  their 
ancestry  must  have  been  widely  different,  the  regions  in 
which  they  live  have  been  isolated  from  one  another  for 
countless  years,  and  yet  they  have  each  got  to  a  “  practically 
rodent  ”  type  of  dentition.  Of  extinct  Lemurs  little  is 

f1)  Skull  of  a  placental  rodent  (Capybara),  showing  general  character  of 
a  rodent’s  dentition. 


TEE  TEETH  OF  MAMMALIA. 


297 


known,  and  of  the  ancestry  of  Cheiromys  nothing ;  but  in 
the  compact  group  of  Marsupials,  still  living  in  Australia, 
we  are  able  to  dimly  see  some  of  the  progressive  steps  which 
seem  to  tend  towards  this  rodent  form  of  dentition.  In 
Australia,  roughly  speaking,  there  were  nothing  but  Mar- 

Fig.  124  0). 


supials ;  in  Madagascar  more  Lemurs  than  anything  else  ; 
and  in  each  case,  out  of  the  material  at  hand,  natural  selection 
has  manufactured  a  “rodent  ”  dentition. 

At  the  same  time  the  force  of  inheritance  is  seen  in  each 
of  them  retaining  characteristics  of  the  groups  whence  they 
have  been  derived,  so  that  underlying  the  primd  facie 
resemblance  in  the  teeth,  there  are  points  in  their  several 


(')  A.  Milk  teeth  of  the  Lenrarine  Cheiromys,  with  the  permanent  in¬ 
cisors  just  coming  into  place.  It  differs  from  any  Rodent  by  having  many 
milk  teeth,  i.  Permanent  incisor.  i  2.  Posterior  deciduous  incisor, 
c.  Deciduous  canine.  d,  d  2.  Deciduous  molars.  1.  Lower  permanent 

incisor.  I  2.  Lower  deciduous  canine,  d  a,  d  b.  Lower  deciduous  molar. 

!  ...... 

B.  Reduced  outline  figure  of  its  permanent  dentition,  in  which  it  closely 
mimics  the  true  rodents.  • 


298 


A  MANUAL  OF  DENTAL  ANATOMY 


dentitions  whereby  the  wombat  shows  its  marsupial  affinities, 
and  the  Aye-aye  its  quadrumanous  affinities. 

An  example  of  the  same  sort  of  thing  is  seen  in  the 
occurrence  of  hinged  teeth  in  various  families  of  fish,  (see 
p.  218)  in  which  the  requirements  of  a  hinge  and  of  a  means 
for  restoring  the  bent-down  tooth  to  the  upright  position  are 
attained  by  different  mechanism  according  to  the  difference 
in  the  raw  material,  if  such  an  expression  may  be  allowed. 

The  approximation  to  a  rodent  type  of  dentition  by  a 
number  of  widely  different  animals  has  led  to  the  suggestion 
being  made,  that  it  does  not  follow  that  all  existing  Rodents 
have  had  a  common  origin.  Thus  Oscar  Schmidt  (“Mam¬ 
malia,”  Internat.  Scientif. series, p.  291)  writes  : — “Acompari- 
son  of  the  very  different  shapes  of  the  molars  in  the  Rodents 
among  one  another,  and  the  approximation  of  many  genera — 
not  as  yet  decided  Rodents — to  the  Rodent  type  (for  instance 
the  Wombat,  the  fingered  animal  (Aye-aye),  and  the  rock 
coney)  render  it  extremely  probable  that  even  our  present 
Rodents  are  not  of  one  and  the  same  origin.  The  fact 
remains,  animals  of  different  derivation  having  attained  a 
similar  exterior,  succeed  extremely  w^ell  in  the  struggle  for 
existence,  or  even  better  in  their  endeavour  to  obtain  food. 
Unlike  as  they  may  be,  in  one  point  they  are  incontestably 
alike,  i.e.  in  the  development  of  continuously  growing  incisors.” 

In  addition  to  those  modifications  which  are  of  direct  use 
to  the  individual  in  the  way  of  assisting  in  the  procuring  of 
food,  &c.,  any  character  which  would  enable  one  male  to  get 
an  advantage  over  other  males,  and  so  render  him  more 
certain  to  propagate  his  kind,  will  be  sure  to  be  transmitted 
and  intensified. 

Thus  we  can  understand  how  the  males  of  some  species 
have  become  ornamented ;  how  the  males  of  many  birds 
have  come  to  sing  ;  and,  what  is  of  more  immediate  concern 
to  us,  how  the  males  of  some  animals  have  become  possessed 
of  weapons  which  the  females  have  not.  The  possession  of 


THE  TEETH  OF  MAMMALIA. 


299 


weapons  by  the  male  is  strikingly  exemplified  in  the  teeth 
of  animals.  The  males  of  many  frugivorous  monkeys  have 
canine  teeth  much  larger  than  those  of  the  females;  they 
are  cut  late,  coincidently  with  the  attainment  of  sexual 
maturity,  and  are  useful  to  their  possessors  as  weapons  in 
their  combats  with  other  males.  The  male  narwal  has  its 
single  elongated  tusk ;  the  male  dugong  has  tusk-like  incisors ; 
in  the  respective  females  these  same  teeth  are  insignificant. 

But  the  most  striking  instance  of  the  teeth  being  modi¬ 
fied,  so  as  to  serve  as  weapons  for  sexual  combat,  is  afforded 
by  some  members  of  the  group  of  ruminants,  amongst  whom, 
as  Cuvier  long  ago  pointed  out,  those  which  are  armed  with 
horns  have  no  canine  teeth,  and  vice  versd — a  generalisation 
which,  although  subject  to  slight  exceptions,  remains  upon 
the  whole  true. 

The  male  musk-deer  (Moschus  moschiferus)  has  canine 
teeth  of  enormous  length,  while  it  is  quite  without  horns 
(see  fig.  125) ;  the  female  has  no  canine  teeth.  The  male 
muntjak,  which  has  very  short  horns,  has  canine  teeth,  but 
of  much  smaller  size  than  those  of  the  musk-deer.  Other 
examples  of  hornless  deer  furnished  with  canine  teeth  are  to 
be  found  in  Swinhoe’s  water-deer  (Hydropotes  inermis)  and. 
in  the  Elaphodus  cephalophus  (which  has  very  small 
antlers)  a  Chinese  deer  more  recently  discovered,  and  in 
the  Tragulidae.  It  is  obvious  that  males  furnished  with 
weapons  more  powerful  than  their  fellows,  will  be  more 
likely  to  prove  victorious  in  their  battles,  to  drive  away  the 
other  males,  to  monopolize  the  herd  of  females,  and  so  to 
transmit  their  own  peculiarities  to  offspring,  which  will 
again  be  favoured  in  the  same  way.  Thus  it  is  very  easy 
to  see  how,  amongst  gregarious  animals,  the  development  of 
teeth  serving  as  sexual  weapons  is  likely  to  be  favoured,  gene¬ 
ration  after  generation,  until  canines  as  highly  specialised  as 
those  of  the  musk-deer,  or  the  wild  boar,  are  attained  to. 

It  will  suffice  to  indicate  to  the  reader  that  he  must  be 


&  WALTEf 


300 


A  MANUAL  OF  DENTAL  ANATOMY. 


prepared  to  find  that  the  teeth  are  profoundly  susceptible 
of  modification,  but  that,  amid  all  their  varied  forms,  the 
evidences  of  descent  from  ancestors  whose  teeth  departed 
less  from  the  typical  mammalian  dentition  are  clearly  trace¬ 
able  in  the  existence  of  rudimentary  teeth  and  other  such 
characters.  And,  although  it  is  by  no  means  probable  that 
we  have  recognised  more  than  a  part  of  the  agencies  which 

Fig.  125  f1). 


are  at  work,  natural  selection  and  sexual  selection  appear 
to  be  competent  to  produce  most  of  the  phenomena  of  modi¬ 
fication  observed.  There  remains  one  other  influence,  much 
more  obscure  in  its  nature,  to  be  touched  upon,  namely, 
“ correlation  of  growth”  or  “  concomitant  variation.”  When 
we  find  that  when  horns  are  developed,  canine  teeth  are 
absent ;  or  that,  after  a  boar  has  been  castrated,  his  tusks 
cease  to  grow,  although  we  may  be  quite  unable  to  conceive 
the  precise  manner  in  which  the  one  thing  influences  the 
other,  we  can  see  that  there  is  a  consistency  in  the  develop¬ 
ment  of  the  sexual  weapon  ceasing  coincidently  with  the 
destruction  of  the  sexual  apparatus,  or  in  the  fact  that 
two  kinds  of  weapon  are  not  developed  in  the  same  animal. 


P)  Cranium  of  Mosclius,  showing  the  long  canine  tooth. 


THE  TEETH  OF  MAMMALIA. 


301 


But  there  are  some  correlations  of  growth  of  a  still  more 
recondite  nature,  in  which  the  connection  is  less  obvious. 
Of  this  nature  is  the  relation  which  exists  between  pecu¬ 
liarities  of  the  skin  and  of  the  teeth :  the  Edentata,  abnormal 
in  their  skins,  are  different  from  most  other  Mammalia  in 
their  teeth ;  whales,  yet  more  aberrant  in  the  nature, 
of  their  skins,  have  only  rudimentary  teeth,  in  the  place  of 
which,  after  birth,  plates  of  whalebone  are  found. 

Mr.  Darwin  (“Animals  and  Plants  under  Domestication,”) 
has  collected  a  number  of  curious  instances  of  relations 
existing  between  hair  and  teeth.  In  general  terms  it  may 
be  said  that  any  great  abnormality  in  the  hair  goes  hand 
in  hand  with  an  abnormalitv  of  the  teeth.  Thus,  there  is  a 
breed  of  dogs  found  in  Turkey  which  are  almost  hairless, 
and  vdiich  have  very  few  teeth,  their  dentition  being  reduced 
to  a  single  molar  on  each  side,  together  with  a  few  imperfect 
incisors  ;  and  in  the  human  subject  inherited  baldness  has 
been  often  found  to  be  associated  with  inherited  deficiency 
of  the  teeth. 

But  vTe  must  not  go  further  than  to  say,  that  great 
abnormality  of  hair  goes  hand  in  hand  with  abnormality  of 
teeth,  for  examples  have  just  been  given  of  absence  of  hair  and 
absence  of  teeth  ;  and,  on  the  other  hand,  redundance  of  hair 
has  in  several  cases  been  accompanied  by  absence  of  teeth. 

Thus,  in  the  case  of  the  now  famous  hairy  family  of 
Burmah,  the  peculiarity  of  silky  hair  being  developed  over 
the  face  vTas  transmitted  to  a  third  generation,  and  in  each 
case  the  teeth  were  very  deficient  in  number.  A  year  or 
twro  ago  a  hairy  man  and  his  son,  said  to  have  come  from 
the  interior  of  Russia,  wrere  exhibited  in  London,  and  they 
were  also  almost  toothless.^) 

(J).  The  man’s  mouth  exemplified  the  dependence  of  the  growth  of  the 
jaw  upon  the  presence  of  teeth.  Ordinarily  the  increase  in  size  between 
childhood  and  adult  age  takes  place  by  a  backward  elongation,  which 
allows  for  the  successive  development  and  eruption  of  the  molars  behind 


302 


A  MANUAL  OF  DENTAL  ANATOMY. 


A  good  many  years  ago  a  hairy  woman  (Julia  Pastrana) 
was  exhibited  in  London,  of  whom  it  has  commonly  been 
reported  that  she  had  an  excessive  number  of  teeth.  Certain 
it  is  that  her  mouth  was  very  prominent,  and  that  she  was 
described  as  “  dog-faced  ”  and  “  pig-faced,”  but  models  have 
been  presented  to  the  Odontological  Society  by  Mr.  Hepburn, 
which  are  indisputably  known  to  be  models  of  her  mouth, 
and  these  do  not  show  any  excessive  number  of  teeth.  The 
teeth,  at  least  such  of  them  as  can  be  seen,  are  enormously 
large,  but  the  mouth  is  affected  with  general  hypertrophy 
of  the  gums  and  alveolar  processes  to  such  a  degree,  that 
onty  a  few  of  the  teeth  can  be  made  out. 

But  this  does  not  make  her  case  the  less  interesting  to 
the  odontologist,  for  in  the  huge  teeth,  the  enormous  papilla) 
of  the  gum,  and  the  redundant  hairs  on  the  face,  we  have 
evidence  of  a  disposition  to  hypertrophies  of  the  integument 
affecting  in  different  places  the  different  tegumentary  appen¬ 
dages  which  happen  to  be  there.  And  that  the  teeth  are 
dermal  appendages  has  been  shown  at  a  previous  page  (sec 
page  2). 


He  would  indeed  be  a  rash  man  who  ventured  to  assert 
that  he  had  recognised  all  the  agencies  which  are  at  work 
in  the  modelling  of  animal  and  vegetable  forms  ;  but  it  is 
safe  to  say  that,  at  the  present  time,  we  are  acquainted  with 
“  natural  selection,”  or  “  survival  of  the  fittest,”  an  agency 
by  which  variations  beneficial  to  their  possessors  will  be 
preserved  and  intensified  in  successive  generations ;  of 
“  sexual  selection,”  which  operates  principally  by  enabling 
those  possessed  of  certain  characters  to  propagate  their  race, 
while  others  less  favoured  do  not  get  the  opportunity  of  so 
doing ;  of  “  concomitant  variation  ”  between  different  parts 


the  space  occupied  by  the  temporary  teeth.  But  this  man  never  had  any 
true  molars,  and  no  such  backward  elongation  of  the  jaw  had  ever  taken 
place,  so  that,  though  he  was  a  full-sized  man,  his  jaw  was  no  larger  than 
a  child's. 


THE  TEETH  OF  MAMMALIA. 


303 


of  the  body,  an  agency  much  more  recondite  in  its  opera¬ 
tions,  but  by  which  agencies  affecting  one  part  may  second¬ 
arily  bring  about  alterations  in  some  other  part. 

And  operating  in  the  contrary  direction,  we  have  a  certain 
fixity  of  organization,  so  that  the  power  of  inheritance  is 
constantly  asserting  itself  by  the  retention  of  parts  which 
have  become  useless,  for  a  time  at  all  events,  and  by  the 
occasional  reappearance  of  characters  which  have  been  lost. 

Some  rather  contradictory  statements  have  been  made  as 
to  the  direct  effect  of  high  feeding,  improvement  of  breed,  &c. 
upon  the  cutting  of  the  teeth,  early  maturity  being  of  course 
one  of  the  aims  of  the  improvers  of  farm  stock. 

With  regard  to  horses,  neither  high  feeding  nor  improved 
breed  seems  to  have  made  any  difference,  e.g.,  a  Highland 
pony  at  five  years  has  as  full  a  mouth  as  the  most  pampered 
horse.  But  in  cows  it  seems  to  be  different — thus  Highland 
cattle  have  all  the  permanent  teeth  at  four-and-a-half  or  five 
years  of  age,  whereas  some  improved  breeds  have  a  full 
mouth  at  three  years  (Williams,  “British  Dental  Association 
Journal,”  April,  1882). 

Prof.  Brown  (“Journ.  Boy.  Agricult.  Soc.,”  1881,  where 
may  be  found  much  valuable  information  on  this  subject,) 
has  been  unable  to  trace  any  change  in  thirty  years,  though, 
if  the  older  writers  were  accurate,  a  real  acceleration  has 
taken  place  over  much  longer  periods. 

He,  however,  quite  denies  that  high  feeding,  of  a  litter  of 
pigs  for  example,  will  produce  any  immediate  effect,  and 
strongly  lays  down  that  their  dentition  is  a  reliable  test  of  age. 

Even  were  it  otherwise,  there  are  many  naturalists  who, 
with  Prof.  Weissmann,  think  that  acquired  qualities,  such  as 
this  would  be,  are  never  transmitted. 

Allusion  has  been  made  to  these  great  biological  questions 
with  the  view  of  helping  the  student  to  have  patience  to 
j  master  descriptions  of  minute  points,  of  which  he  does  not 
;  at  the  moment  see  the  bearing,  by  giving  him  confidence 


304 


A  MANUAL  OF  DENTAL  ANATOMY. 


that  there  are  no  characters  so  trivial  but  that  they  may 
throw  very  important  light  upon  the  remote  parentage  and 
the  line  of  descent  of  the  creature  under  examination.  And 
as  a  farther  incentive  to  painstaking  and  minute  observa¬ 
tion,  it  may  be  added,  that  things  which  are  rudimentary, 
and  therefore  inconspicuous,  are  often  just  the  things  which 
happen  to  teach  us  most ;  for  being  of  no  present  use,  they 
are  not  undergoing  that  rapid  change  in  adaptation  to  the 
creature’s  habits  which  may  be  going  on  in  organs  which  are 
actively  employed. 


THE  HOMOLOGIES  OF  THE  TEETH. 

A  superficial  survey  of  the  teeth  of  those  mammals  which 
possess  two  sets  of  teeth  (diphyodonts)  will  indicate'  that, 
notwithstanding  the  apparent  anomalies  brought  about  by 
adaptive  modifications,  a  close  correspondence  between  the 
several  teeth  of  different  animals  exists.  That  is  to  say,  we 
can  generally  identify  incisors,  premolars,  and  molars ;  nay, 
more,  when  an  animal  has  less  than  the  full  typical  number 
of  a  particular  class  of  teeth,  we  can  ordinarily  say  with 
certainty  which  of  them  it  is  that  are  absent. 

As  it  is  impossible,  or  at  least  inconvenient,  to  avoid  the 
use  of  the  term  “typical”  dentition,  it  will  be  well  to  explain 
at  the  outset  what  is,  and  what  is  not,  meant  by  it. 

That  the  great  majority  of  biologists  reject  utterly  the 
“  archetype  ”  theory,  by  which  all  those  resemblances  which 
really  exist  were  referred  to  the  influence  of  a  sort  of  gene¬ 
ralised  “  pattern  ”  animal,  according  to  the  model  of  which 
all  other  animals  were  fashioned,  has  already  been  mentioned : 
this,  then,  is  what  is  not  meant  by  a  “  typical  ”  dentition. 
What  is  meant,  is  a  form  so  simplified,  so  little  modified  in 
any  special  direction,  that  we  can  conceive  it  to  be  near  to  a 
common  parent  form  whence,  by  progressive  modification  in 


305 


THE  TEETH  OF  MAMMALIA': 


successive  generations,  other  forms  have  been  derived.  We 
cannot  point  to  any  mammalian  dentition  at  present  known! 
to  us,  and  say  this  may  have  been  the  parent ;  this  is  a 
typical  form  of  mammalian  dentition;  but  we  do  know  many 
fossil  forms  which  approximate  to  it  more  closely  than  do  any 
at  present  in  existence,'  and  as  transitional  forms  of  animals, 
and  animals  of  highly  generalised  characters,  are  every  day 
coming  to  light,  we  do  not  doubt  that  such  forms  once  did 
actually  exist,  and  may  one  of  these  days  be  found.  But  it 
would  probably  be  as  far  back  as  Palaeozoic  times,  whereas 
our  oldest  mammalian  fossils  are  Mesozoic.1  Absolute 
proof  would  be  obtainable  only  if  we  could  refer  to  its  place 
every  mammal  that  had  ever  existed,  and  show  every  step  in 
the  series  of  modifications  by  which  the  ultimate  divergence 
of  dentition  was  effected.  But  evidence  far  short  of  absolute 
demonstration  serves  to  satisfy  us  on  most  points,  and  there 
is  sufficient  evidence  available  to  enable  us  to  say  with  some 
confidence  that  our  “typical”  or  parent  mammalian  dentition 
was,  so  far  as  the  numbers  of  the  several  kinds  of  teeth  go, 


.3  1  4  3.. 

1  -  c  -  prm  -  m  -  =  44. 


And  when  there  are  less  than  forty-four  teeth,  as  has  been 
already  mentioned,  we  can  in  most  cases  say  which  they 
are  that  are  absent. 

Thus,  taking  a  certain  bear  and  a  baboon  (each  having 
two  premolars  only  on  each  side),  we  are  able  to  decide,  by 
comparison  with  allied  creatures,  that,  in  the  case  of  the 
bear,  it  is  the  second  and  third  premolars  which  are  wanting, 
the  first  and  fourth  remaining ;  while  in  the  baboon  it  is  the 
first  and  second  which  are  wanting,  the  third  and  fourth 
being  present.  By  homology  we  mean  such  correspondence 
as  is  above  indicated ;  a  correspondence  which  might  almost  be 
expressed  as  a  relationship  by  descent,  in  the  individual  teeth. 


f)  But  since  writing  the  above,  Prof.  Marsh  has  announced  the  discovery 
of  numerous  mammalian  fossils  in  Cretaceous  formations. 


306 


A  MANUAL  OF  DENTAL  ANATOMY. 


Homology,  then,  is  almost  equivalent  to  identity  of  origin, 
or,  at  all  events,  to  similarity  of  origin  ;  but  it  by  no  means 
necessarily  involves  identity  or  even  similarity  in  the  pur¬ 
pose  to  which  a  thing  is  ultimately  applied — a  fact  which 
will  be  further  illustrated  in  speaking  of  canine  teeth. 

The  homologies  of  the  teeth  may  be  treated  under  two 
heads  :  the  one,  the  homologies  of  the  teeth  in  their  relation 
to  other  parts  of  the  body,  and  the  other,  their  more  especial 
homologies,  or  their  relation  to  one  another. 

The  relation  of  the  teeth  to  the  skin,  which  we  express  by 
calling  them  “  dermal  appendages,”  as  well  as  the  epidermic 
nature  of  the  enamel,  and  the  dermic  nature  of  the  dentine 
have  been  sufficiently  discussed  at  former  pages,  so  that 
we  may  at  once  pass  to  the  homologies  of  the  teeth  with 
one  another. 

Teeth  are  divided  into  incisors,  canines,  premolars,  and 
molars,  but  these  classes  do  not  all  admit  of  quite  satis¬ 
factory  definition.  Incisors  are  defined  as  teeth  implanted 
in  the  intermaxillary  bone,  a  definition  which  has  the  merit 
of  being  precise  ;  and  on  the  whole  there  is  a  certain  resem¬ 
blance  running  through  incisor  teeth  in  most  animals,  but 
the  definition  of  lower  incisors  as  being  the  corresponding 
teeth  in  the  lower  jaw  is  a  good  deal  less  satisfactory,  because 
they  are  not  situate  upon  any  distinct  bone.  And  it  has 
even  been  denied  that  there  can  be  a  true  homology  between 
a  maxillary  and  a  mandibular  tooth. 

Molars  are  teeth  at  the  back  of  the  mouth,  which  come 
up  behind  the  milk  teeth  (when  there  are  any),  and  which 
are  generally  subservient  to  grinding  the  food. 

Premolars  are  teeth  in  front  of  the  molars,  usually  differ¬ 
ing  from  them  by  being  more  simple  in  form  and  being 
smaller,  and,  in  most  animals,  by  having  displaced  deciduous 
predecessors.  But  they  are  not  always  simpler  in  form, 
nor  smaller  ( e.g .,  in  the  horse),  nor  do  they  always 
displace  deciduous  predecessors  {e.g.,  they  do  not  all  do  so 


THE  TEETH  OF  MAMMALIA . 


307 


in  the  Marsupials),  so  that  this  definition  is  not  absolutely 
precise.  Still,  as  a  matter  of  practice,  it  is  usually  easy  to 
distinguish  the  premolars,  and  the  division  into  premolars 
and  molars  is  useful. 

Any  objection  that  can  be  raised  to  the  name  of  pre molar 
on  the  score  of  a  short  logical  definition  being  impossible, 
applies  with  tenfold  force  to  the  canines.  (Cf.  Messrs* 
Moseley  and  Lankester,  Journ.  Anat.  and  Physiology,  1869.) 

The  nearest  approach  to  a  good  definition  is  that  which 
describes  the  canine  as  the  next  tooth  behind  the  intermax¬ 
illary  suture,  provided  it  be  not  far  behind  it ;  and  the 
lower  canine  as  the  tooth  which  closes  in  front  of  the  upper 
canine. 

A  great  deal  of  confusion  has  arisen  out  of  the  twofold 

*>' 

sense  in  which  the  word  “  canine  ”  is  used  :  if  it  were  always 
applied  to  designate  the  first  tooth  in  the  maxilla  of  the 
typical  mammalian  dentition  quite  irrespective  of  its  size, 
Ac.,  and  the  lower  tooth  closing  in  front  of  it,  no  objection 
to  its  employment  could  be  made,  inasmuch  as  it  would 
designate  truly  homologous  organs. 

But  it  so  happens  that  the  tooth  in  question  is,  in  a  very 
large  number  of  familiar  animals,  developed  to  a  large  size 
and  sharply  pointed  for  use  as  a  weapon,  and  so  with  the 
word  canine  there  comes  to  be  associated  a  teleological 
idea;  and  hence  we  are  dissatisfied  with  calling  the  first 
maxillary  tooth  “canine,”  when  there  is  some  other  tooth 
which  is  doing  its  work. 

On  the  other  hand,  if  we  are  to  leave  out  of  court  all 
considerations  as  to  size,  purpose  to  which  it  is  to  be 
applied,  and  so  forth,  there  is  nothing  left  to  make  it 
deserving  of  a  name  distinguishing  it  from  the  four  teeth 
behind  it.  So  we  must  be  content  with  some  such  state¬ 
ment  as  the  following. 

A  very  large  number  of  animals,  notably  the  Carnivora, 
have  one  tooth,  situated  a  little  way  from  the  front  of  the 

x  2 


308 


A  MANUAL  OF  DENTAL  ANATOMY. 


mouth,  developed  to  an  unusual  length  and  sharply  pointed, 
for  use  as  a  weapon.  The  tooth  which  has  undergone  this 
adaptive  modification  is  usually  the  first  which  lies  in  the 
maxillary  bone ;  in  fact,  the  foremost  of  the  premolar 
series  •  but  it  occasionally  happens  that  it  is  some  other 
tooth  which  has  undergone  this  modification.  When  we 
use  the  term  canine  we  should  generally  mean  a  tooth  so 
modified,  and  generally,  but  not  always,  should  be  alluding” 
to  the  same  tooth,  i.e.,  to  the  tooth  which  in  the  typical 
mammalian  dentition  comes  next  behind  the  outermost 
incisor — the  first  of  the  premolars,  if  we  allow  five  premolars 
instead  of  four. 

It  would  practically  be  very  inconvenient  to  abolish  the 
term  canine  ;  but  it  should  be  borne  in  mind  that  its  signi¬ 
ficance  is  merely  equivalent  to  “  caniniform  premolar,”  and 
that  in  describing  the  dog’s  dentition  (p.  328)  we  should  be 
less  liable  to  be  misinterpreted,  were  we  to  say  that  it  has 
five  premolars,  of  which  the  first  is  caniniform.  To  those 
who  accept  the  doctrine  of  evolution  it  is  not  needful  to  say 
more,  as  it  is  hardly  possible  to  resist  the  conclusion  that 
the  teeth  of  the  parent  forms  were,  like  those  of  the  present 
monophyodonts,  not  much  differentiated  from  one  another. 
Then,  as  animals  diverged  and  became  modified  in  accordance 
with  their  requirements,  their  teeth  would  become  so  far 
differentiated  that  they  would  admit  of  being  classified. 
Thus  the  Carnivora  would  have  attained  to  a  stage  of 
differentiation  in  which  the  canine  is  functionally  certainly 
deserving  of  a  distinction,  whereas  along  other  lines  of 
descent,  differentiation  having  not  proceeded  so  far,  or  having 
proceeded  in  a  somewhat  different  direction,  it  would  not 
merit  a  distinctive  appellation. 

But  it  will  be  desirable  to  point  out  a  few  instances  of 
the  difficulties  to  which  those  anatomists  are  committed  who 
call  some  tooth  a  “  canine  ”  in  every  case  where  a  tooth  is 
situated  in  the  maxillary  bone,  close  behind  the  suture 


THE  TEETH  OF  MAMMALIA. 


which  connects  it  with  the  intermaxillary  hone,  whether 
that  or  any  other  tooth  be  large  and  pointed,  “  caniniform  ” 
or  not. 

In  typical  Ruminants,  the  upper  jaw  lacks  both  incisors 
and  canines  (with  certain  exceptions,  for  which  see  p.  299),  but 
in  front  of  the  lower  jaw  there  are  grouped  together  eight 
teeth,  closely  fitted  together,  and  of  almost  exactly  similar 
size  and  shape.  The  outermost  pair  of  these  teeth  are 
called  canines,  because  (i.)  in  some  allied  species  the  tooth 


Fig.  126  (*). 


in  this  situation  is  more  pointed ;  (ii.)  because  this  tooth 
shuts  in  advance  of  the  upper  canine  when  the  mouth  is 
closed  (in  those  allied  creatures  which  have  an  undoubted 
upper  canine)  ;  (iii.)  because  it  is  cut  later  than  the  others 
(Owen). 

These  three  reasons  are  weak,  because  (i.)  form  is  a 
very  unsafe  guide  to  homology,  and  as  to  the  lateness  of  its 
development  (iii.),  it  succeeds  to  the  third  incisor,  by  Pro¬ 
fessor  Owen’s  own  showing,  after  about  the  same  lapse  of 
time  which  separated  the  eruption  of  the  second  and  third 
incisors.  Moreover,  Oreodon,  an  extinct  Ruminant  with 

p)  Oreodon  Culbertsonii  (after  Leidy).  It  will  be  observed  that  in  the 
tipper  jaw  the  four  premolars  of  the  typical  mammalian  dentition  are 
behind  the  “  canine, ”  but  that  in  the  lower  jaw  the  tooth  which  would 
fulfil  the  functions-  of  a  canine  is  the  first  of  these  four,  find  therefore  is 
rot  the  corresponding  tooth  to  the  i  *  canine  ”  in  the  upper  jaw.  '  ■ ,  ; 


A  MANUAL  OF  DENTAL  ANATOMY. 


310 


caniniforai  teeth,  has  the  eight  incisors  in  the  lower  jaw  in 
addition  to  a  caniniform  tooth ,  which  is  the  fifth  tooth  counting 
from  the  front.  With  reference  to  the  relative  positions  of 
the  upper  and  lower  teeth,  determining  which  is  and  which 
is  not  “  the  canine,”  (ii.)  no  one,  looking  at  the  dentition 
of  Oreodon,  would  be  inclined  to  hesitate  which  teeth  he 
should  call  “  canines ;  ”  yet  the  lower  caniniform  tooth 


Fig.  127  0). 


shuts  behind  the  upper,  and  therefore,  according  to  this 
test,  it  is  not  a  true  canine. 

In  the  Lemurs  there  are  similarly  eight  procumbent  teeth 
occupying  the  front  of  the  lower  jaw,  of  which  the  outer¬ 
most  pair  are  called  canines,  although  not  in  the  smallest 
degree  meriting  that  name  for  any  other  reason  than  that 
they  close  in  front  of  the  caniniform  tooth  of  the  upper  jaw> 
for  they  are  just  like  the  other  incisors. 

But  it  is  in  the  Insectivora,  which  in  some  respects 
represent  an  ancient  and  generalised  mammalian  form,  that 
the  greatest  difficulties  occur. 

To  the  mole  no  less  than  four  dental  formulae  have  been 
assigned,  all  turning  upon  the  identification  of  the  canine. 

(!)  Upper  and  lower  teeth  of  the  common  mole.  In  it,  just  as  in 
Oreodon,  the  teeth  which  fulfil  the  functions  of  canines  are  not  corre¬ 
sponding  teeth  in  the  upper  and  lower  jaws. 


THE  TEETH  OF  MAMMALIA , 


311 


The  difficulty  is  this  :  The  upper  tooth,  which  looks  like  a 
canine,  has  two  roots,  and  is  implanted  (and  its  deciduous 
predecessors  also  lie  :  Spence  Bate)  within  the  limits  of 
the  premaxillary  bone.  And  besides  this,  the  lower  tooth, 
which  answers  the  purpose  of,  and  looks  like,  a  canine, 
closes  behind  instead  of  in  front  of  the  great  upper  tooth, 

Ericulus  has  a  sharp,  long-,  two-fanged  tooth,  in  pattern  of  crown 
an  enlarged  premolar,  in  position  of  upper  canine,  and  no  canini- 
form  tooth  in  lower  jaw. 

Centetes  has  typical  canines,  like  a  Carnivore. 

Hemicentetes.  The  so-called  canine,  differs  in  no  respect  from  the 
premolars  behind  it. 

Evinaceus.  So-called  upper  canine,  two-rooted,  and  like  the  pre* 
molars  which  follow  behind  it. 

Gymnnra.  Upper  canine-like  tooth  has  two  roots  ;  a  single-rooted 
lower  pointed  tooth  closes  in  front  of  it. 

Macroscelis  and  Petrodromus.  The  third  or  outermost  incisor  is 
two-rooted,  long,  and  sharp,  and  plays  the  part  of  a  canine. 
Potanwgale.  A  small  tooth,  in  no  respect  different  from  the  other 
premolars,  is  called  a  “  canine.” 

In  some  of  the  groups  no  tooth  has  been  lengthened  and 
pointed,  so  as  to  serve  as  a  canine  ;  in  'others  it  is  the  wrong 
tooth,  i.e.,  not  the  same  tooth  as  in  the  Carnivora,  or  as  in 
other  Insectivora.  Consequently,  in  the  Insectivora  the 
elevation  of  a  tooth  into  caniniform  length  and  character  is 
a  mere  adaptive  modification,  which  may  affect  an  incisor? 
or  a  premolar,  or  no  tooth  at  all. 

A  large  number  of  the  small  Mesozoic  mammals  had  two- 
rooted  canine  teeth  (Marsh). 

It  appears  to  me  that  the  result  of  all  investigations  inta 
the  homologies  of  mammalian  teeth  may  be  summed  up 
somewhat  in  the  following  manner. 

The  evidence  of  a  common  pattern,  which  is  traceable  in 
incisors,  canines,  premolars,  and  molars,  would  seem  to 
indicate  that  their  special  forms  have  been  all  derived 
|  from  modifications  of  some  much  more  simple  form,  and 
that  if  we  are  ever  to  find  what  might  be  called  a  parent 


312 


A  MANUAL  OF  DENTAL  ANATOMY. 


mammalian  dentition,  it  will  be  nearly  “homodont  that 
is  to  say,  the  several  teeth  will  not  differ  much  from  ore 
another  in  size  and  shape,  just  as  we  see  to  be  the  case  in 
the  dolphin  or  the  armadillo. 

If  we  were  able  to  place  in  unbroken  series  all  the  den¬ 
titions  through  which,  by  progressive  modification,  the 
original  almost  homodont  dentition  had  passed  into  a 
highly  specialised  dentition,  like  that,  say,  of  the  cat,  it 
would  be  a  matter  of  impossibility  to  fix  upon  any  point 
where  we  should  be  justified  in  asserting  that  here  the 
homodont  dentition  has  recently  become  heterodont :  at  this 
point,  for  the  first  time,  we  have  incisors,  canines,  molars. 

The  earliest  mammalian  dentitions  known  to  us  carry  us 
back  no  further  than  Mesozoic  times,1  and  of  the  Mesozoic 
mammals  we  may  say  that  they  had  mostly  smooth  cerebral 
hemispheres,  no  inflection  of  the  angle  of  the  lower  jaw,  and 
forty-four  or  more  teeth  :  of  these  the  canines  had  two  roots, 
and  the  premolars  and  molars  were  little  differentiated  from 
one  another.  The  generalised  members  of  these,  whom  Prof. 
Marsh  proposes  to  group  under  the  new  order  Pantotheria, 
were  perhaps  the  ancestors  of  the  modern  specialised 
Insectivora  (American  Journal  of  Science,  April,  1887). 

The  usual  pattern  of  tooth  was  tricuspid,  the  central 
cusp  greatly  preponderating,  but  it  remains  uncertain 
whether  these  Mesozoic  mammals  were  Marsupials  or 
.Placentals,  or  whether  they  may  be  generalised  forms  from 
which  both  have  been  subsequently  derived. 

The  Amphitherium  (lower  jaw  alone)  is  one  of  the 


earliest  dentitions  known, 


coming 


from  the  Jurassic 


formations  ;  it  had  sixteen  teeth,  which,  so  far  as  their 
forms  can  tell  us,  were 

i  —  n  pm 


1 


m 


6 


.  '  .  V  '  *  • 

>  But  from  the  Purbeck  bone  bed  quite  a  number  of  forms 

(-1)  See  footnote  on- p.  3051,  ■  - 


313 


THE  TEETH  OP  MAMMALIA. 


have  been  described,  some  of  which  have  several  incisors, 
and  a  general  insectivorous  type  of  dentition  (Polyproto- 
donts);  others  have  a  single  long-pointed  incisor  on  each  side 
of  the  median  line  (Diprotodonts)  like  existing  kangaroos, 
and  compressed  blade-shaped  premolars,  so  that  even  at 
this  period  much  differentiation  had  already  taken  place, 
and  we  are  far  from  generalised  parent  forms. 

It  is  noted  by  0.  Schmidt  that  specialisation  of  teeth 
often  goes  hand  in  hand  with  specialisation  of  the  extremities. 

A  large  number  of  extinct  Ungulata  had  the  full  typical 
number  of  mammalian  teeth,  viz.,  forty-four,  and  in  some 
the  individual  teeth,  incisors,  canines,  premolars,  and 
molars,  passed  into  one  another  by  insensible  gradations, 
and  contiguous  teeth  were  but  little  differentiated  from  one 
another.  Professor  Flower  has  described  and  figured  such 
an  extinct  Ungulate  under  the  name  of  Homalodontotherium 
(Philos.  Trans.  1874).  It  is  exceedingly  interesting  to  find 
that  far  back  in  geological  time  the  dentitions  were  more 
generalised,  both  carnivorous  and  herbivorous  mammals  of 
the  Eocene  period  usually  possessing  the  full  typical  number 
of  teeth,  and  displaying  less  of  special  modification ;  but  the 
few  forms  of  life  which  have  been  handed  down  in  a  fossil 
state  do  not  as  yet  offer  us  by  any  means  an  unbroken  chain 
of  forms  differing  from  one  another  by  progressive  modifica¬ 
tion,  except  in  a  few  cases  :  thus  the  ancestry  of  the  horse 
is  now  comparatively  completely  known  to  us. 

Bearing  in  mind  that  the  several  kinds  of  teeth  have 
'probably  a  common  origin,  the  homological  differentiation 
in  the  incisors,  premolars,  and  molars  may  be  advantageously 
admitted,  and  made  use  of  as  a  basis  for  comparing  and 
classifying  the  teeth  of  different  animals.  It  is  usually  said 
that  when  incisors  are  missing  from  the  full  typical  number, 
i  they  are  lost  from  the  outer  end  of  the  series  :  that  is  to 
j  say,  if  there  is  but  one  incisor  it  is  l1 ;  if  two,  Ix  and  I2. 

There  are  many  exceptions  to  this  <?,</.,  the  first  incisor 


3l  4 


A  MANUAL  OF  DENTAL  ANATOMY. 


is  the  first  to  disappear  in  the  otter,  walrus,  and  some  few 
others,  and  a  question  has  been  raised  as  to  the  homologies 
of  man’s  two  incisors. 

When  premolars  are  missing,  it  is  said  that  they  are  lost 
from  the  front  of  the  series.  This  is  generally  true,  but 
there  are  many  exceptions,  of  which  the  following  may  be 
given. 

In  many  bears  the  second  premolar  is  often  lost,  as  is 
also  the  third,  but  the  first  and  the  fourth  are  very  constant ; 
this  is  also  true  of  some  bats.  ( 1 ) 

To  make  this  more  clear,  Mr.  Oldfield  Thomas  proposes  to 
write  out  in  full  the  dentition,  thus  : — 

Bear  : — 


i 


1.2.3 
1.2.3  ° 


pm 


1.0. 0.4  1.2,0 

1. 0.0.4  m  1.2.3 


There  seems  good  reason  to  suppose  that  although  modern 
marsupials  have  but  three  premolars,  the  original  number 
was  four,  as  in  placental  mammals ;  and  among  the  Dasy- 
uridse,  a  study  of  the  genus  Phascologale,  in  which  pm2 
and  pm 3  are  very  constant,  but  pm4  variable  down  to 
being  a  minute  and  functionless  tooth  in  one  species,  has 
shown  that  in  Dasyurus,  with  its  two  premolars,  it  is  pm4 
that  has  gone  for  one. 

And  a  comparison  of  many  specimens,  in  one  of  which 
(Phascologale)  four  premolars  were  present,  pm2  being 
smaller  than  the  others,  and  a  skull  of  Dasyurus  in  which  a 
rudimentary  tooth  was  present  between  its  two  premolars, 
indicates  that  the  other  which  has  disappeared  was  pm2. 


Thus  Dasyurus  has  pm 
and  Tliylacinus  pm 


1.0. 3.0 
1.0. 3.6’ 
1.0. 3. 4 


1 .0.3.4 


(1)  This  is  ascertained  by  the  examination  of  allied  forms,  in  which  the 
third  premolar  is  found  to  be  so  small  as  to  be  rudimentary. 


THE  TEETH  OF  MAMMALIA. 


315 


A  difficulty  at  times  occurs  in  deciding  whether  a  tooth 
is  to  be  regarded  as  a  premolar,  or  as  a  milk  tooth,  as  there 
are  many  so-called  permanent  teeth  which  are  lost  early  in 
the  lifetime  of  the  animal. 

Professor  Flower  gives  an  instance  of  this  in  the  hippo¬ 
potamus  :  the  first  premolar  appears  with  the  milk  teeth ; 
it  probably  had  no  predecessor,  and  is  shed  in  middle  life. 
But  in  allied  forms  the  corresponding  tooth  remains  in  place 
throughout  the  creature’s  life. 

The  wart-hog  is  a  conspicuous  example  of  the  early  loss 
of  teeth  which  clearly  belong  to  the  permanent  series, 
all  the  teeth,  (premolar  and  molar)  in  front  of  the  last 
great  molar  being  cast  off,  and  the  dentition  ultimately 
reduced  to — 

•  A  l_  !_ 

i  3  o-j  m  "j 

That  general  correspondence  wffiich  is  found  to  exist 
between  the  dentitions  of  various  animals,  extends  also  to 
the  patterns  of  individual  teeth,  so  that  we  are  able  to  trace 
out  the  various  stages  by  which  complexity  of  pattern  has 
been  arrived  at. 

In  what  might  be  termed  a  typical  tooth  wre  should  have 
a  single  central  pulp  cavity  surrounded  by  a  body  of  hard 
dentine ;  over  the  crown  this  is  coated  by  enamel,  whilst 
the  whole,  crown  and  root,  would  be  invested  by  a  layer  of 
cement. 

The  layer  of  coronal  cement  may  be  so  thin  as  to  be 
merely  rudimentary,  as  in  Man  or  the  Carnivora ;  or  the 
investment  with  enamel  may  be  only  partial,  as  upon  the 
front  of  a  Bodent  incisor;  or  a  tooth  may  be  composed 
j  solely  of  a  mass  of  hard  unvascular  dentine,  as  in  the  teeth 
i  cf  the  Wrasses. 

And  just  as  endless  varieties  of  teeth  may  be  produced 
1  by  the  suppression,  or  partial  suppression,  of  certain  of  the 
tissues,  so  differences  may  be  brought  about  by  the  occur- 


,316 


A  MANUAL  OF  DENTAL  ANATOMY. 


rence  of  other  than  the  three  usual  tissues.  Thus  the 
remains  of  the  central  pulp  cavity  often  becomes  occupied 
by  calcified  pulp,  forming  “  osteodentine ;  ”  this,  which 
occurs  in  man  as  an  almost  pathological  condition,  is  per¬ 
fectly  normal  in  many  animals ;  in  the  sperm  whale,  for 
instance,  or  in  the  constantly  growing  teeth  of  the  sloth, 
the  central  axes  of  which  are  occupied  by  dentine  permeated 
by  medullary  canals. 

It  is  not  so  much  the  complexities  induced  by  variation 
in  minute  structure  that  concern  us  here,  as  those  brought 
about  by  the  arrangement  of  the  different  tissues. 

If  we  take  a  simple  conical  tooth  with  one  cusp,  such  as 
a  canine,  and  grind  or  wear  down  its  apex  till  the  terminal 
portion  of  enamel  is  removed,  its  blunted  end  will  present  a 
more  or  less  circular  area  of  dentine,  surrounded  by  a  rim 
of  enamel.  If  we  imagine  a  tooth  with  four  long  similar 
cusps,  we  shall  at  a  certain  stage  of  wear  have  four  such 
areas,  while  eventually,  as  the  tooth  gets  worn  down  below 
the  level  of  the  bases  of  the  cusps,  there  will  come  to  be  a 
single  larger  area  of  dentine  surrounded  by  enamel.  Thus 
in  those  teeth  the  grinding  surfaces  of  which  are  rendered 
complex  in  pattern  by  the  presence  of  several  cusps,  the 
pattern  changes  from  time  to  time  as  the  tooth  wears  down ; 
while  the  addition  of  thick  cementum  filling  up  the  inter¬ 
spaces  of  the  cusps,  adds  a  further  element  of  complexity,  as 
is  seen  in  the  teeth  of  most  herbivorous  creatures.  The 
change  of  pattern  induced  by  the  wearing  down  of  the  surface 
to  a  lower  level  is  well  and  simply  illustrated  by  the 
“  mark  ”  of  the  incisor  teeth  of  a  horse. 

In  an  uncut,  and  therefore  perfectly  unworn  tooth, 
the  condition  of  the  apex  may  be  compared  to  the  finger 
of  a  glove,  the  tip  of  which  has  been  pushed  hi  or  ipr 
vaginated.  The  depression  so  formed  is,, like  the  rest  of 
the  surface,  coated  with  enamel,  and  with,  a  thin  layer  of 
cepaentum.  .  .  o  ...  A 


THE  TEETH  OF  MAMMALIA . 


a  17. 


When  the  tooth  is  worn  down  to  a  considerable  extent, 
we  have  a  field  of  dentine,  in  the  centre  of  which  is  an 
oval  ring  of  enamel ;  within  this  a  space  filled  with  the.' 
debris  of  food,  <fco.  This  constitutes  the  mark,  and  as  the 


tooth  becomes  further  worn  down,  below  the  level  of  the 
bottom  of  the  pit,  the  mark  disappears,  and  a  plain  area  of 
dentine  results. 

Interesting  as  have  been  the  discoveries  made  of  late 
years  in  mammalian  palseontology,  it  is  not  as  yet  by  any 
means  possible  to  say  that  all  complex  mammalian 
teeth  may  be  considered  to  have  been  derived  from 
i  simple  conical  tooth  ;  though  the  pattern  of  some,  for 
example,  of  the  molars  of  the  horse,  may  be  traced  back 
j  n  increasing  simplicity  through  a  number  of  parent  forms. 

Virchow,  in  relating  a  case  in  which  the  place  of  an  upper 

II  ....  4 

(1)  Horse  incisor,  in  longitudinal  section. 

(2)  Horse’s  incisors,  showing  the  mark  at  various  ages. 


318 


A  MANUAL  OF  DENTAL  ANATOMY. 


molar  had  been  taken  by  three  peg-shaped  denticles  with 
separate  roots,  suggests  that  this  may  have  been  due  to 
atavism,  and  that  multicuspid  teeth  may  have  been 
formed  by  the  coalescence  of  several  separate  teeth  of  the 
homodont  parent  dentition.  But  a  study  of  the  evolution  of 
complex  forms  of  tooth  crown  from  simple  ones  seems  to 
negative  this  hypothesis.  And  Dr.  H.  F.  Osborn  (American 
Naturalist,  Dec.  1888)  has  made  an  important  contribution 
to  this  subject  by  wide-spread  investigations,  the  result  of 
which  is  to  indicate  that  a  trituberculate  molar  was  almost 
as  universal  among  Mesozoic  mammals  as  a  pentadactyle 
foot.  The  three  cusps  were  arranged  in  a  triangle,  the 
single  cusp  lying  to  the  inner  side  (antero-internal)  in  the 
upper,  and  to  the  outer  in  the  lower  molars ;  and  the  whole 
triangle  of  cusps  of  the  lower  tooth  passed  in  front  of  that 
of  the  upper  in  closure  of  the  mouth,  the  teeth  of  the  two 
jaws  thus  alternating  rather  than  meeting  grinding  surface 
to  grinding  surface.  He  believes  that  these  “  three  primary” 
cusps  “  formed  a  central  stage  from  which  the  great  majority 
of  recent  molar  types  have  diverged  by  the  addition, 
modification,  and  reduction  of  cusps  :  we  must  except  the 
Monotremes,  the  Edentates,  and  possibly  the  Cetaceous, 
although  there  is  considerable  evidence  that  the  Cetacean 
molars  were  once  of  the  Triconodont  type.” 

Believing  that  a  simple  cone  was  the  original  form,  a 
trituberculate  form  had  been  reached  by  the  Mesozoic 
period,  and  these  three  primary  cusps  may  be  traced  and 
their  homologies  established  in  later  and  more  complex  molar 
patterns  ;  the  added  or  secondary  cusps  following  certain 
lines  and  allowing  of  the  establishment  of  their  homologies, 
though  with  less  certainty. 

It  is  very  interesting  to  note  that  even  when  teeth  have 
become  flat-topped  and  quadri  or  quinque-tuberculate,  the 
primary  triangles  of  the  upper  and  lower  teeth  retain  their 
old  relative  position,  i.e.  alternate  with  one  another. 


THE  TEETH  OF  MAMMALIA. 


819 


Dr.  Osborn  proposes  a  nomenclature 1  for  the  cusps, 
slightly  less  cumbrous  than  “  antero-external,”  &c.,  &c.,  but 
whether  it  will  obtain  currency  time  must  show  :  he  gives 
names  to  six  cusps  on  both  upper  and  lower  teeth,  i.e.,  to 
three  supplementary  ones  besides  the  primary  ones. 

A  very  instructive  series  of  comparisons  of  the  molar 
teeth  of  Insectivora  has  been  made  by  Mr.  Mivart  (Journal 
of  Anat.  and  Physiol.,  1868),  pointing  out  that  within 
the  limits  of  this  group  a  great  variety  of  patterns  is  met 
with,  the  several  modifications  being  connected  by  transi¬ 
tional  forms. 

It  wxmld  appear  that  upon  the  molar  teeth  (upper)  of 
Insectivora  there  are  four  principal  cusps  (lettered  a,  b,  c.  d, 
in  the  figure)  which  are  more  or  less  connected  by  ridges ; 
such  simple  teeth  are  met  with  in  the  elephant  mice 
(Macroscelides)  and  hedgehog.  The  cingulum  is  wTell 
developed  in  most  of  the  group,  and  the  further  complexity 
of  the  crowns,  which  often  bristle  with  sharp  points,  is 
brought  about  by  the  elevation  of  the  cingulum  into  long 
sharp  points,  equalling,  or  exceeding  in  length,  the  principal 
cusps  of  the  tooth. 

Thus  in  Urotrichus,  a  Japanese  creature  having  affinities 
with  the  mole,  the  external  cingulum  is  elevated  into  three 
distinct  pointed  cusps,  united  by  ridges  with  the  two  prin¬ 
cipal  cusps,  an  arrangement  which  gives  a  sort  of  W  pattern 
to  the  surface,  while  to  the  inner  side  the  cingulum  forms 
another  cusp,  so  that  there  are  in  all  eight  cusps ;  the 
common  mole  has  the  third  cusp  developed  from  the  outer 
cingulum,  but  its  two  inner  principal  cusps  are  fused  together 

1  Protocone  =  Antero-internal  cusp  of  upper  molar  ;  ?  homologue  of  the 
single  cusp  of  primitive  tooth. 

Paracone=:  Antero-external  cusp  of  upper  molar, 
i  Metacone  =  Postero-external  cusp  of  upper  molar. 

I  Protoconid  =  Antero-external  cusp  of  lower  molar. 

Paraconid,  metaconid  =  corresponding  cusps  of  lower  teeth. 


32Q 


A  MANUAL  OF  DENTAL  ANATOMY . 


and  lose  their  distinctiveness*  The  suppression  and  fusion  of 
cusps  is  carried  to  a  much  greater  extent  in  the  compressed 
teeth  of  the  iridescent  mole  (Chrysochloris),  but  there  are 
intermediate  forms  which  render  it  easy  to  identify  its 
reduced  parts  with  those  corresponding  to  them  in  the  mole 
or  in  Urotriclms. 


Fig.  130  (*). 


AFC 


Speaking  generally,  it  may  be  said  that  new  cusps  are 
added  to  the  number  already  existing,  by  the  cingulum 
becoming  elevated  into  points  ;  it  is  not  very  unusual  to  see 
subsidiary  cusps  obviously  originating  in  this  way  upon 
human  molars. 

Ridges  may  variously  connect  the  cusps ;  and  the  coales¬ 
cence  of  two  or  more  cusps  to  form  an  exceedingly  elevated 
point  is  illustrated  by  the  carnassial  tooth  of  Carnivora ;  to 
this  transformation  certain  marsupial  teeth  form  the  clue,  as 
they  afford  unquestionable  evidence  of  such  coalescence  by 
a  gradational  series  of  small  modifications  in  this  direction 
occurring  in  allied  creatures. 

A  common  pattern  of  tooth  is  formed  by  the  junction  of 
the  two  anterior  and  two  posterior  cusps  by  simple  ridges ; 

(!)  Upper  molar  teeth  of  (A)  Urotrichus  ;  (B)  Mole  ;  and  (C)  Chryso¬ 
chloris.  The  four  principal  cusps  are  lettered  a ,  b,  c,  cl,  in  each  of  the 
figures.  In  A  the  cingulum  has  been  elevated  so  as  to  form  four  additional 
cusps  on  the  exterior  of  the  tooth,  and  one  additional  cusp  on  the  interior. 
B  and  C  show  the  fusion  of  certain  of  these  cusps,  and  the  consequent 
diminution  in  their  number.  (From  Mivart.) 


THE  TEETH  OF  MAMMALIA. 


321 


i 


and  the  cingulum  may  connect  the  outer  ends  of  these  two 
ridges ;  such  a  tooth  is  seen  in  the  Tapir,  and  in  the 
Palseotherium.  By  the  varied  obliquity  of  these  ridges, 
and  by  the  introduction  of  secondary  inflections,  patterns 
apparently  dissimilar  are  arrived  at. 

In  the  molar  tooth  of  the  horse,  arrived  at  by  a  modifi¬ 
cation  of  the  Palseotherium  type,  we  have  a  surface  con¬ 
stantly  kept  rough  by  the  varying  hardness  of  its  different 
constituents. 

In  a  worn  tooth,  we  have  upon  a  general  field  of  dentine 
two  islands  of  cementum,  bounded  by  tortuous  lines  of 
enamel,  and  on  the  inner  side  a  sort  of  promontory  of 

Fig.  131  (*). 


dentine,  bounded  by  enamel.  The  tortuous  lines  of  enamel 
by  virtue  of  their  hardness  will,  at  all  stages  of  wear,  be 
more  prominent  than  the  dentine  or  the  cementum,  and 
will  hence  maintain  the  efficiency  of  teeth  as  grinders. 

The  patterns  of  grinding  surface  thus  produced,  are  very 
constant  for  allied  species,  so  that  an  individual  tooth  of  a 
herbivore  may  sometimes  be  correctly  referred  to  its  genus, 
and  always  to  its  family. 

But  as  it  will  be  necessary  to  recur  to  this  subject  from 
time  to  time,  it  will  suffice  for  the  present  to  point  out  that 

f1)  Molar  tooth  of  Horse,  showing  the  characteristic  pattern  of  its 
grinding  surface. 

Y 


I 


322 


A  MANUAL  OF  DENTAL  ANATOMY. 


such  correspondences  do  exist,  and  that  all  the  complexities 
of  pattern  found,  may,  in  practice,  be  reduced  to  some  few 
types. 

The  development  of  additional  cusps  from  up-growths  of  the 
cingulum,  and  the  suppression  or  fusion  of  pre-existing  cusps, 
may  be  traced  by  a  comparison  of  the  teeth  of  allied  animals, 
and  thus  connecting  links  are  found  between  patterns  at 
first  sight  very  dissimilar.  The  order  Proboscidea  affords, 
however,  so  instructive  an  instance  of  the  manner  in  which 
an  exceedingly  complex  tooth  has  been  derived  from  a 
simple  one,  that  it  may  be  mentioned  in  this  place  as  an 
example. 

The  tooth  of  the  elephant  is  so  strikingly  unlike  other 
teeth  that  it  might  at  first  sight  be  supposed  that  it  is 


Fig.  132  0). 

b  cl  e 


more  essentially  different  than  is  really  the  case.  The  clue 
to  its  nature  is  afforded  by  the  teeth  of  an  extinct  Pro¬ 
boscidian,  the  Mastodon.  If  we  take  as  our  starting  point 
the  second  true  molar  of  one  of  the  Mastodons  (Tetralo- 
phodon)  we  find  its  crown  to  be  made  up  of  four  strongly 

(l)  Second  upper  molar  of  Mastodon  (longirostris),  from  Falconer. 
About  one-eighth  natural  size.  The  four  transverse  ridges,  b,  c,  d,  e.  are 
seen  to  be,  to  some  extent,  divided  into  outer  and  inner  divisions  by  a 
longitudinal  cleft,  much  less  deep  than  the  transverse  indentation.  At 
the  front  there  is  a  slight  elevation  of  cingulum  into  a  “talon  ”  (a),  and  a 
similar  one  at  the  back  of  the  teeth  ;  by  its  further  elevation  additional 
ridges  or  cusps  would  be  formed. 


THE  TEETH  OF  MAMMALIA. 


323 


pronounced  transverse  ridges,  the  summits  of  which  are 
made  up  of  rounded  eminences  (whence  the  name  Mastodon, 
from  imuttos,  a  nipple).  The  three  transverse  ridges  coalesce 
at  their  bases,  and  the  crown  is  supported  upon  a  number 
of  roots  corresponding  to  the  ridges. 

If  we  take  the  next  tooth,  or  the  third  true  molar,  the 
general  character  remains  the  same,  save  that  there  are  five 
ridges,  and  indications  of  as  many  roots  ;  still  the  general 
correspondence  of  the  ridges  with  the  cusps  of  less  aberrant 
teeth  is  obvious. 

The  crown  is  coated  by  enamel,  over  which  there  is  a 
thin  layer  of  cement,  which  does  not  fill  up  the  whole 
interval  between  the  ridges. 

Thus  the  tooth  is  not  a  very  aberrant  one ;  it  is  obviously 
nothing  more  than  a  tooth  in  which  the  somewhat  numerous 

Fig.  133  {l). 


cusps  are  connected  by  transverse  ridges,  and  are  very  long 
and  strongly  pronounced. 

To  convert  the  tooth  of  a  mastodon  into  that  of  an 
elephant,  we  should  have  to  multiply  the  number  of  ridges, 
to  further  increase  their  depth,  to  fill  up  solidly  the  inter¬ 
spaces  between  them  with  cementum,  and  to  stunt  the 
roots.  The  completed  tooth  of  an  elephant  is  a  squarish 
or  rather  oblong  mass,  from  the  base  of  which  spring  con¬ 
tracted  and  stunted  roots.  Jt  consists  of  a  common  pulp 


(!)  Molar  Tooth  of  an  Asiatic  Elephant,  showing  the  transverse  plates  of 
dentine  bordered  by  enamel , 


324 


A  MANUAL  OF  DENTAL  ANATOMY. 


cavity,  small  in  proportion  to  the  bulk  of  the  tooth,  and 
deep  down  in  the  mass  ;  from  it  many  thin  laminae  are 
sent  up  towards  the  surface,  each  forming  the  core  of  an 
area  of  dentine  enclosed  by  enamel ;  and  the  interspaces  of 
these  exaggerated  cusps  are  solidly  filled  in  by  cementum. 

Between  the  Mastodon  and  the  Indian  Elephant  are  a 
number  of  transitional  forms  in  which  we  are  able  to  trace 
the  gradual  modification  of  the  not  excessively  aberrant 
tooth  of  the  Mastodon  into  the  very  peculiar  huge  molar 
of  the  Indian  Elephant, 

The  numerous  transverse  plate  of  the  elephant’s  grinders 
are  united  by  dentine  at  their  bases,  and  a  common  pulp 
cavity  and  truncated  roots  are  formed ;  but  in  this  last 


respect  the  molar  teeth  of  the  Capybara  depart  still  farther 
from  the  ordinary  type,  for  being  molars  of  persistent 
growth,  their  numerous  transverse  plates  of  dentine  and 
enamel  do  not  become  continuous,  and  there  is  no  common 
pulp  cavity.  It  is  as  though  in  an  elephant’s  grinder  the 
plates,  which  are  for  a  long  time  distinct,  never  coalesced, 
but  continued  to  grow  on  separately,  being  united  with  their 
fellows  by  cementum  only. 

It  has  been  suggested  (J.  A.  Ryder,  Proc.  Acad.  Nat. 
Sciences,  Philadelphia,  1878),  that  the  pattern  of  the  molar 
teeth  of  herbivora  is  the  result  of  the  extent  and  direction 
of  the  excursions  of  the  mandible  when  it  is  in  use,  and  so 
depends  upon  the  form  of  the  glenoid  cavity  and  of  the 

f1)  Molar  of  Capybara,  showing  the  transverse  plates  of  dentine  and 
enamel  united  to  one  another  by  cementum.  , 


THE  TEETH  OF  MAMMALIA 


825 


I 


condyle,  and  that  hence  the  greatest  modification  is  to  be 
found  nearest  to  the  articulation,  where  the  greatest  force 
is  exerted. 

Thus  “bunodont”  animals,  i.e.  those  that  have  rounded 
conical  cusps  upon  their  short-rooted  teeth,  have  a  cylindrical 
condyle ;  selenodonts,  or  those  with  crescentic  ridges  on  the 
molars,  have  a  condyle  which  is  expanded  and  plane,  wdiile 
lophodonts,  or  those  with  transversely  ridged  teeth,  have  a 
globular  condyle. 

That  there  is  some  correspondence  between  the  condyle, 
the  movement  of  the  jaw,  and  the  form  of  the  teeth  is  a 
fact,  but  it  is  not  so  easy  to  see  how  it  is  brought  about. 

The  simple  mechanical  explanation  that  the  teeth  are 
so  to  speak  drawn  out  into  these  forms,  whether  in  one  or 
in  ten  thousand  generations,  does  not  commend  itself  to  my 
mind.  For  that  portion  of  the  tooth  which  is  subject  to 
these  direct  influences  is  hard  and  rigid,  and  its  form, 
whatever  it  be,  is  unalterable  :  in  order  to  alter  the  form  of 
a  masticating  surface  by  direct  mechanical  means,  the  in¬ 
fluence  would  have  to  be  brought  to  bear  upon  the  teeth 
while  they  are  yet  soft,  when  they  are  still  buried  within 
the  jaw. 

And  it  is  believed  by  many  evolutionists  that  acquired 
properties,  i.e.,  those  acquired  by  the  individual  under  out¬ 
side  influences  after  its  birth,  are  never  inherited,  but  that 
nothing  is  inherited  save  variations,  the  capacity  for  which 
pre-existed  in  the  ovum  and  the  sperm  cell. 

Without  going  the  length  of  altogether  subscribing  to 
this  doctrine,  the  difficulty  of  seeing  how  a  mechani- 
callyracquired  character  should  be  inherited,  is  at  least 
as  great  as  the  difficulty  of  realising  how  advantageous 
specialisations  should  be  carried  further  and  intensified  by 
the  ordinary  laws  of  natural  selection. 


326 


A  MANUAL  OF  DENTAL  ANA  TOMY. 


THE  JVIILK  DENTITION. 

Some  thirty  years  ago  Professor  Owen  called  attention  to 
the  fact  that  those  mammals  in  whom  the  teeth  situated  in 
different  parts  of  the  mouth  were  alike  in  form  (homodonts), 
developed  only  one  set  of  teeth,  and  to  indicate  this  charac¬ 
teristic  he  proposed  for  them  the  term  “  monophyodonts.” 
Those,  which,  on  the  contrary,  had  teeth  of  different  size 
and  form  in  various  parts  of  the  mouth  (heterodonts),  de¬ 
veloped  two  sets  of  teeth ;  a  “  milk  set,  which  was  dis¬ 
placed  by  a  permanent  set,  and  this  peculiarity  he  expressed 
by  the  term  “  diphyodonts.”  As  originally  set  forth,  the 
terms  homodont  and  monophyodont  were  interchangeable, 
for  they  designated  the  same  groups  of  animals ;  in  the 
same  way  heterodont  was  an  equivalent  for  diphyodont. 

But  although  this  is  true  of  a  large  number  of  animals,  it 
is  not  true  of  all,  and  it  becomes  necessary  to  note  some  of 
the  exceptions. 

The  nine-banded  armadillo  (Tatusia  peba)  is  a  true  homo¬ 
dont  :  its  teeth  are  all  very  nearly  alike,  they  are  simple  in 
form,  and  they  grow  from  persistent  pulps.  Yet  it  has 
been  shown  by  Bapp,  Gervais,  and  Professor  Flower,  to 
have  a  well  developed  set  of  milk  teeth,  retained  until  the 
animal  is  of  nearly  full  size. 

Thus  it  is  a  true  diphyodont,  at  the  same  time  that  it  is 
a  true  homodont  mammal.  But  no  milk  dentition  has  been 
observed  in  the  sloths,  nor  indeed  at  present  has  it  been 
seen  in  any  other  armadillo  (except  the  doubtfully  distinct 
T.  Klapperi) ;  nor  have  milk  teeth  been  found  in  any  Ceta¬ 
cean,  so  that  the  rest  of  the  homodont  animals  are,  so  far  as 
we  know,  really  monophyodont. 

Nor  is  it  absolutely  true  that  monophyodonts  are  all 
homodont :  thus  the  rudimentary  teeth  of  Balsenoptera  are 
heterodont  (see  p.  342). 

Upon  the  whole,  our  information  respecting  the  “  milk  ” 


THE  TEETH  OF  MAMMALIA. 


327 


or  deciduous  dentition  is  defective  ;  but  much  light  has 
been  thrown  upon  the  subject  by  the  investigations  of 
Professor  Flower  (Journal  of  Anatomy  and  Physiology, 
1869,  and  Transactions  Odontological  Society,  1871),  of 
whose  papers  I  have  made  free  use  in  this  chapter. 

The  perpetual  replacement  of  teeth  lost,  or  shed  in  regular 
course,  which  characterises  the  dentition  of  fish  and  reptiles, 
i  finds  no  parallel  in  the  case  of  mammals,  none  of  whom 
develop  more  than  two  sets  of  teeth. 

Just  as  homodont  mammals  as  a  rule  develop  but  one  set 
of  teeth,  so  heterodont  mammals  as  a  rule  develop  two  sets 
of  teeth,  though  exceptions  to  this  rule  may  be  found. 

The  deciduous  or  milk  set  of  teeth  may  be  of  any  degree 
of  completeness  ;  the  milk  teeth  in  man  answer  the  require- 
j  ments  of  the  child  up  to  the  age  of  seven  years,  and  in  the 
Ungulata  they  commonly  remain  until  the  animal  has 
assumed  its  adult  proportions.  On  the  other  hand,  in 
many  “diphyodont”  animals  the  milk  teeth  disappear  very 
early  indeed,  as  in  the  mole  (see  page  310) ;  whilst  there 
y  are  many  instances  of  the  milk  teeth  being  absorbed  in  utero. 
So  that  in  the  extent  to  which  the  milk  teeth  are  developed, 
the  greatest  variability  is  found  to  exist. 

A  perfectly  typical  milk  dentition  represents,  upon  a 
reduced  scale,  the  adult  dentition  of  the  animal,  with  the 
exception  only  that  sexual  differences  are  but  feebly  marked, 
if  indeed  they  are  at  all  present. 

Thus,  as  a  general  rule,  the  hindmost  of  the  milk  teeth 
bear  more  resemblance  to  the  true  molars  which  come  up 
behind  them,  than  they  do  to  the  premolars  which  come  up 
from  below  to  displace  them,  which  latter  are  generally  of 
simpler  form. 

In  what  may  be  termed  the  normal  arrangement,  each 
tooth  of  the  milk  series  is  vertically  displaced  by  a  tooth  of 
\  the  permanent  series ;  but  plenty  of  examples  may  be 
found  of  particular  milk  teeth  which  have  no  successors, 


328 


A  MANUAL  OF  DENTAL  ANATOMY. 


and,  on  the  contrary,  of  individual  permanent  teeth  which 
have  never  had  a  deciduous  predecessor. 

It  has  already  been  mentioned  that  amongst  homodonts 
no  succession  of  teeth  has  been  observed  in  the  Cetacea, 


Fig.  135  0). 


nor  in  any  other  of  the  Edentata,  save  the  armadillo ; 
amongst  lieterodonts  there  are  several  Rodents  which  have 
no  deciduous  teeth,  e.g.,  the  rat;  the  dugong  has  probably 
deciduous  incisors,  but  no  other  milk  teeth  ;  the  elephant 
has  no  vertical  succession,  save  in  the  incisors. 

Among  Marsupials,  which  are  true  heterodonts,  there  is 
only  one  milk  molar  on  each  side  in  each  jaw;  this  is  always 

(’)  Permanent  and  milk  dentitions  of  a  Dog ;  the  latter  was  well 
developed.  Nat.  size. 

(2)  Permanent  and  milk  dentition  of  a  seal  (PhocaGrreenlandia).  Nat.  size. 


THE  TEETH  OF  MAMMALIA. 


329 


displaced  by  the  third  or  last  premolar 1 ;  but  the  milk 
tooth  varies  in  the  extent  to  which  it  is  developed  from 
being  rudimentary  in  Thylacinus,  probably  absent  altogether 


Fig.  137  (2). 


in  Dasyurusp  and  Phascolarctus,  to  being  a  large  tooth 
retained  in  full  use  till  the  animal  is  nearly  full  grown  in 
Hypsiprymnus. 

Within  the  group  Carnivora,  the  dog  and  many  others 
have  a  thoroughly  well  developed  set  of  milk  teeth,  which 


( 1 )  Probably  this  is  really  pm4. 

(2)  Permanent  and  milk  dentition  of  an  Elephant  Seal  (Cystophora 
proboscidea). 

(3)  Teeth  of  the  truly  monophyodont  Grampus  (Orca  capensis).  (These 
four  figures  are  copied  from  Prof.  Flower’s  paper). 

(4)  See,  for  a  more  detailed  account  of  the  milk  dentition  of  Mar¬ 
supials,  the  chapter  relating  to  them. 


330 


A  MANUAL  OF  DENTAL  ANATOMY. 


do  service  for  some  time ;  in  the  bear  the  milk  teeth  are 
relatively  smaller,  and  are  shed  very  early ;  in  the  seal  the 
milk  teeth  are  rudimentary,  functionless,  and  are  absorbed 
before  birth,  so  that  in  the  specimen  figured  the  milk  incisors 
had  already  disappeared  (see  Fig.  136). 

In  the  elephant  seal  the  milk  teeth  are  yet  more  rudi¬ 
mentary,  and  the  difference  between  its  dentition  and  that 
of  the  monophyodont  homodont  cetacean  (Grampus)  is  not 
great ;  an  observation  which  is  the  more  interesting,  inas¬ 
much  as  this  seal  in  other  characters  than  its  teeth  ap¬ 
proaches  towards  the  cetacean  group.  From  these  facts, 
which  are  well  indicated  in  the  accompanying  figures,  Pro¬ 
fessor  Flower  argues  that  the  permanent  set  of  teeth  of 
diphyodonts  correspond  to  the  single  set  of  monophyodonts, 
so  that  the  milk  dentition,  when  it  exists  at  all,  is  some¬ 
thing  superadded. 

Whether  this  be  so  is  a  question  difficult  to  determine ; 
from  the  facts  advanced  by  Professor  Flower,  while  they 
stood  alone,  most  people  would,  with  little  hesitation,  concur 
with  his  conclusion,  and  this  interpretation  is  endorsed  by 
Mr.  Oldfield  Thomas,  but  the  history  of  the  development  of 
the  teeth  interposes  a  difficulty. 

The  tooth  germ  of  the  milk  tooth  is  first  formed,  and  the 
tooth  germ  of  the  permanent  tooth  is  derived  from  a  portion 
(the  neck  of  the  enamel  germ)  of  the  formative  organ  of  the 
milk  tooth  (see  Fig.  68).  Again,  in  most  of  those  animals 
in  which  there  is  an  endless  succession  of  teeth,  such  as  the 
snake,  the  newt,  or  the  shark,  each  successive  tooth  germ  is 
derived  from  a  similar  part  of  its  predecessor,  the  natural 
inference  from  which  would  be  that  the  permanent  set, 
being  derived  from  the  other,  was  the  thing  added  in  the 
diphyodonts. 

The  question  cannot  be  finally  settled  until  we  know  more 
.of  the  development  of  the  teeth  of  the  monophyodont  Cetacea: 
thus  it  might  turn  out  that  in  them  also  there  are  abortive 


I 


THE  TEETH  OF  MAMMALIA. 


331 


germs  of  milk  teeth  formed,  which  do  not  go  on  so  far  as 
calcification,  but  which  do  bud  off,  as  it  were,  germs  for  per¬ 
manent  teeth ;  if  such  should  prove  to  be  the  case,  this 
would  bring  their  teeth  into  close  correspondence  with  those 
of  the  elephant  seal. 

The  investigation  of  these  questions  is  further  complicated 
by  the  fact  that  there  are  quite  numerous  instances  of  “  per¬ 
manent  ”  teeth,  that  is  teeth  unquestionably  belonging  to 
the  second  set,  which  are  shed  off  early,  and  do  not  remain 
in  place  through  the  lifetime  of  the  animal ;  an  example  of 
this  is  to  be  found  in  the  Wart  Hog  (Phacochserus),  which 
loses  successively  all  its  premolars  and  the  first  and  second 
true  molars,  the  last  true  molar  alone  being  truly  per¬ 
sistent. 

In  the  Ornithorhyncus  wre  have  an  example  of  the  loss  of 
teeth,  which  doubtless  in  some  ancestral  form  were  both 
more  numerous  and  more  persistent,  and  the  Cyclostomatous 
fish  (see  page  228)  appear  also  to  be  instances  of  degradation 
in  this  respect.  So  also  the  seal  would  appear  to  be  in  the 
state  of  having  really  lost  its  milk  dentition  :  indeed,  it  is 
difficult  to  understand  how  upon  the  evolution  hypothesis, 
the  earlier  stages  of  the  introduction  of  a  milk  dentition 
could  be  preserved  and  intensified,  for  they  could  have  been 
of  no  use  to  their  possessors. 

It  is  a  possible  hypothesis  that  the  normal  mammalian 
condition  is  Diphyodont,  and  that  the  Monophyodonts  have 
arrived  at  the  stage  of  having  wholly  lost  their  milk  den¬ 
titions,  whilst  in  others  it  has  lingered  on,  as  in  Tatusia 
peba  in  full  strength,  or  as  in  the  seal,  in  feeble  rudiments. 

There  is  a  reason,  or  some  show  of  a  reason,  for  the  suc¬ 
cession  taking  place  as  farbackasthe  premolars,  and  the  molars 
being  exempt  from  change,  which  so  far  as  I  know,  has  not 
been  noticed  by  any  of  the  many  writers  upon  the  subject. 
In  all  mammals  the  whole  length  of  the  jaw,  at  the  time  of 
birth  and  afterwards,  is  occupied  by  tooth  germs  and  after- 


332 


A  MANUAL  OF  DENTAL  ANATOMY. 


wards  by  teeth  ;  it  is  well  ascertained  that  the  manner  of 
growth  in  the  jaw  is  by  backward  elongation,  and  that  that 
portion  which  is  occupied  by  the  molars  actually  do6s  not 
exist  at  the  time  of  birth.  Tooth  change  might  therefore  be 
expected  to  be  limited,  as  in  fact  it  is,  to  that  portion  of  the 
jaws  which  exists  early,  while  the  animal  is  small ;  milk 
teeth  could  not  exist  in  the  molar  region,  because  during 
their  reign  the  molar  region  itself  does  not  exist. 

Oscar  Schmidt  suggests  that  the  origin  of  milk  teeth  can 
be  traced  back  to  the  shortening  of  the  facial  region,  which 
gave  no  room  for  the  full  number  of  tooth  germs  to  lie 
side  by  side  :  the  result  of  this  crowding  being  that  they 
came  to  lie  one  upon  the  top  of  another,  and  the  teeth  lying 
nearest  to  the  surface,  having  to  be  used  first,  get  developed 
first. 

The  milk  teeth  are  thus  placed  at  a  disadvantage  owing 
to  the  hostile  position  of  their  successors,  and  according  to 
this  view,  the  Marsupials  and  seals  would  have  once 
possessed,  but  have  now  lost  their  milk  teeth. 


Cuvier.  Dents  des  Mammiferes. 

De  Blainville.  Osteographie.  1839 — 1864. 

Owen.  Odontography.  1845. 

Gtebel.  Odontographie.  1855. 

Flower.  Lectures  on  Odontology  (British  Med.  Journal,  1871). 
Oldfield  Thomas.  Philos.  Trans.,  1887. 

Homologies,  &c.,  in  the  Dasyuridae. 

O.  Schmidt.  The  Mammalia.  Internat.  Scientific  Series. 


CHAPTER  IX. 


THE  TEETH  OF  EDENTATA,  CETACEA,  AND  SIRENIA. 

THE  TEETH  OF  EDENTATA  (BrUTA). 

Sloths,  Armadillos,  Ant-eaters. 

The  term  Edentata  was  applied  to  the  animals  of  this 
order  to  indicate  the  absence  of  incisors  (teeth  in  the  inter¬ 
maxillary  bone)  :  though  this  is  true  of  most  of  them,  a  few 
have  some  upper  incisors,  but  the  central'  incisors  are  in  all 
cases  wanting. 

Some  of  them  are  quite  edentulous  ;  this  is  the  case  in 
the  Mutica,  or  South  American  Ant-eaters  (Myrmecophaga 
and  Cyclothurus),  in  which  the  excessively  elongated  jaws 
cannot  be  separated  to  any  considerable  extent,  the  mouth 
being  a  small  slit  at  the  end  of  the  elongated  muzzle. 
Food  is  taken  in  by  the  protrusion  of  an  excessively  long, 
whip-like  tongue,  which  is  covered  by  the  viscid  secretion 
of  the  great  sub-maxillary  glands,  and  is  wielded  with  much 
dexterity.  The  Manis,  or  Scaly  Ant-eater  is  also  edentulous. 

The  Edentata  belong  to  the  monophyodont  or  homodont 
section  of  Mammalia ;  but,  in  some,  certain  teeth  are  more 
largely  developed  than  others,  so  that  we  have  teeth  which 
might  be  termed  canines  ;  and  it  has  already  been  mentioned 
that  one  armadillo,  at  all  events,  is  diphyodont. 

The  teeth  are  of  simple  form,  and  do  not  in  any  marked 
degree  differ  in  the  different  parts  of  the  mouth,  except  only 
by  their  size  (to  this  the  canine-like  tooth  of  the  two-toed 
sloth  is  an  exception).  They  are  all  of  persistent  growth, 


334 


A  MANUAL  OF  DENTAL  ANATOMY . 


and  therefore  no  division  of  parts  into  crown,  neck,  and  root 
is  possible  :  they  consist  generally  of  dentine  and  cement, 
with  sometimes  the  addition  of  vaso-dentine,  into  which 
latter  tissue  the  central  axis  of  the  pulp  is  converted  ;  while 
in  some  members  of  the  order  other  peculiarities  of  structure 
exist  :  thus  in  the  Orycteropus  (Cape  Ant-eater),  dentine 
like  that  of  Myliobates  is  found ;  and  in  the  Megatherium 
hard  dentine,  a  peculiar  vaso-dentine,  and  richly  vascular 
cementum  co-exist  ("see  Fig.  44). 

I  am  not  aware  that  enamel  has  been  seen  upon  the  teeth 
of  any  Edentate  animal,  but  I  found  some  years  ago  that 
the  tooth  germs  of  the  nine-banded  armadillo  were  provided 
with  enamel  organs ;  this,  however,  proves  nothing,  for 
(Philos.  Trans.,  1876)  I  believe  the  presence  of  enamel 
organs  to  be  universal  and  quite  independent  of  any  after 
formation  of  enamel. 

The  teeth  of  the  nine-banded  armadillo  (T.  peba),  will 
serve  to  illustrate  the  character  of  the  dentition  of  the 
class.  They  are  seven  in  number  on  each  side  of  the  jaw,  of 
roundish  form  on  section,  and  those  of  the  upper  and  lower 
jaws  alternate,  so  that  by  wear  they  come  to  terminate  in 
wedge-shaped  grinding  surfaces  :  before  they  are  at  all  worn 
they  are  bilobed,  as  may  be  seen  in  sections  of  the  tooth-germs. 

In  the  accompanying  figure  the  milk  teeth  are  represented, 
and  beneath  them  their  permanent  successors :  the  divari¬ 
cated  bases  of  the  milk  teeth  are  due  to  the  absorption  set 
up  by  the  approach  of  their  successors,  and  not  to  the 
formation  of  any  definite  roots.  Successional  teeth  have 
been  detected  in  this  armadillo  only  (except  also  in  T. 
kappleri,  which  is  perhaps  a  mere  variety) ;  but  material 
does  not  exist  in  our  museums  which  would  enable  us  to 
positively  deny  their  occurrence  in  other  forms. 

Professor  Flower  has  failed  to  discover  any  succession  of 
teeth  in  the  sloths,  and  I  have  myself,  through  the  kindness  of 
the  late  Professor  Garrod,  examined  microscopically  the  jaws 


THE  TEETH  OF  EDENTATA. 


335 


of  a  foetal  Choloepus,  in  which  the  teeth  were  but  little 
calcified,  and  failed  to  detect  any  indication  of  a  second  set 
of  tooth-germs.  The  probability  is,  therefore,  that  they  are 
truly  Monophyodont. 

In  the  armadillos  the  teeth  are  always  of  simple  form  and 
about  thirty-two  in  number,  except  in  Priodon,  which  has  as 
many  as  a  hundred  teeth,  a  number  altogether  exceptional 
among  mammals. 

Sloths  have  fewer  teeth  than  armadillos,  and  these  softer 
in  character,  the  axis  of  vaso-dentine  entering  more  largely 
into  their  composition,  and  forming  as  much  as  half  the  bulk 
of  the  tooth. 

5 

The  two-toed  Sloth  has  j  teeth  in  each  jaw,  and  these  are 


Fig.  139  (*). 


nearly  cylindrical  in  section  and  of  persistent  growth.  In 
the  region  of  the  canine  tooth  is  a  tooth  which  is  of  larger 
size  than  the  rest. 

The  Orycteropus,  or  Cape  Ant-eater,  the  peculiarities  of 
whose  teeth  have  already  been  alluded  to,  has  about  thirty- 
six  teeth  in  all ;  but  these  are  not  all  in  place  at  one  time, 
the  smaller  anterior  teeth  being  shed  before  the  back  teeth 
are  in  place. 

The  true  Ant-eaters  are  all  edentulous.  The  teeth  of 
some  of  the  gigantic  extinct  Edentates  were  a  little  more 

n 

complex  in  form  and  structure  ;  thus  the  teeth  of  the 
Glyptodon  were  divided  by  longitudinal  grooves,  which  in 

(b  Lower  jaw  of  a  young  Armadillo  (Tatusia  peba),  showing  the  milk- 
i  teeth  (a)  in  place,  and  their  successors  ( b )  beneath  them.  From  a 
specimen  in  the  Museum  of  the  Royal  College  of  Surgeons  (after  Flower). 


336 


A  MANUAL  OF  DENTAL  ANATOMY. 


section  rendered  it  trilobed ;  and  the  teeth  of  the  Mega¬ 
therium  were  likewise  marked  by  a  longitudinal  furrow. 

In  their  persistent  growth,  uniformity  of  shape,  and 
absence  from  the  inter-maxillary  bone,  they  strictly  con¬ 
formed  with  the  teeth  of  recent  Edentata. 


THE  TEETH  OF  CETACEA. 

This  order  is  divided  into  two  groups,  namely  the  toothed 
whales  or  Odontoceti  and  the  whalebone  whales  or  Mysti- 
coceti;  these  two  groups  are  sharply  defined  from  one  another. 

No  cetacean  is  known  to  develop  more  than  one  set  of 
teeth,  and  these,  when  present  in  any  considerable  numbers, 
closely  resemble  one  another  in  form. 

The  teeth,  however,  of  the  extinct  Zeuglodon  and  Squalo- 
don  which  have  about  361  teeth  are  heterodont  in  character. 

They  are  usually  composed  of  hard  dentine,  with  an  in¬ 
vestment  of  cement ;  after  the  attainment  of  the  full  dimen¬ 
sions  of  the  teeth  what  remains  of  the  pulp  is  very  commonly 
converted  into  secondary  dentine ;  tips,  and  even  entire 
investments  of  enamel,  are  met  with  in  many  of  the  order. 

The  dentine  of  many  Cetaceans,  e.g.  of  the  sperm  whale, 
is  remarkable  for  the  very  numerous  interglobular  spaces 
which  it  contains ;  these  are  clustered  in  concentric  rows, 
so  as  to  give  rise  to  the  appearance  of  contour  lines.  The 
cement  is  often  of  great  thickness,  and  the  lacunae  in  it  are 
very  abundant ;  its  lamination  is  also  very  distinct. 

In  the  dolphin  the  teeth  are  very  numerous,  there  being 
about  200  ;  they  are  slender,  conical,  slightly  curved  in¬ 
wards,  and  sharply  pointed  ;  as  they  interdigitate  with  one 
another  there  is  very  little  wear  upon  the  points,  which 
consequently  remain  quite  sharp.  The  largest  teeth  are 
those  situated  about  the  middle  of  the  dental  series. 

Many  variations  in  the  number  and  form  of  the  teeth 


THE  TEETH  OF  CETACEA. 


337 


are  met  with  ;  the  porpoise  has  not  more  than  half  the 
number  of  teeth  possessed  by  the  dolphin,  while  the  gram¬ 
pus  has  still  fewer.  The  teeth  of  the  grampus  become 
worn  down  on  their  opposed  surfaces,  and  coincidently 


Fig.  140  (J). 


with  their  wearing  away  the  pulps  become  calcified.  In 
the  Oxford  museum  there  is  a  grampus  in  which,  owing  to 


Fig.  141  (2). 


a  distortion  of  the  lower  jaw,  the  teeth,  instead  of  inter- 
digitating,  became  exactly  opposed  to  one  another ;  the 
consequence  of  this  was  that  the  rate  of  wear  was  greatly 
increased,  and  the  pulp  cavities  were  opened  before  the 
obliteration  of  the  pulp  by  calcification  (3),  so  that  the  pulps 
died  and  abscesses  around  the  teeth  had  resulted. 

In  the  sperm  whale  the  teeth  are  numerous  in  the  lower 
jaw,  but  in  the  upper  jaw  there  are  only  a  few  curved, 

(b  Jaws  of  a  common  Dolphin. 

(2)  Teeth  of  upper  jaw  of  a  Grampus  (Orca),  (after  Professor  Flower). 

(3)  Trans.  Odonto.  Society,  1873.  When  I  published  this  paper  I  was 
not  aware  that  Eschricht  had  previously  published  a  similar  observation. 


338 


A  MANUAL  OF  DENTAL  ANATOMY. 


stunted  teeth,  which  remain  buried  in  the  dense  gum.  The 
teeth  of  the  lower  jaw  are  retained  in  shallow  and  wide  de¬ 
pressions  of  the  bone  by  a  dense  ligamentous  gum,  which, 
when  stripped  away,  carries  the  teeth  with  it.  Every  inter¬ 
mediate  stage  between  this  slight  implantation  and  the 
Avell-developed  stout  sockets  of  the  grampus,  is  met  with  in 
the  Cetacea. 

In  the  bottle-nosed  whale  (Hyperoodon  bidens)  the  only 
large  teeth  present  are  two  conical,  enamel-tipped  teeth  (some¬ 
times  four)  which  remain  more  or  less  completely  embedded 
within  the  gum,  near  to  the  front  of  the  lower  jaw :  in 
addition  to  these  there  are  12  or  13  very  small  rudimentary 
teeth  loose  in  the  gums  of  both  jaws.  (Eschricht,  Lacdpede.) 

The  Ziphoid  cetaceans  present  one  of  the  most  curious 
and  inexplicable  dentitions  to  be  found  in  any  animal.  The 
upper  jaws  are  edentulous,  as  in  the  Hyperoodon,  and  the 
lower  jaws  contain  only  a  single  tooth  upon  each  side  ;  but 
these  teeth  have  attained  to  great  proportions,  measuring  in 
full-grown  specimens  as  much  as  ten  inches  in  length ;  they 
are  thin,  flat,  and  strap-shaped,  straight  for  some  considerable 
part  of  their  length,  and  then  curving  over  towards  each 
other;  they  even  cross  each  other  above  the  upper  jaw  so 
that  they  actually  limit,  and  that  to  a  very  small  amount, 
the  extent  to  which  the  jaws  can  be  opened. 

It  is  not  merely  difficult  to  s.ee  what  use  these  teeth  can 
be,  but  it  is  hard  to  suppose  that  they  can  be  otherwise  than 
actually  detrimental  to  their  possessors  in  the  pursuit  of 
food  ;  but  there  is  some  reason  to  suppose  that  the  presence 
of  well  developed  tusks  is  a  character  of  the  male  sex,  though 
upon  this  point  the  evidence  is  not  quite  complete.  Eemales 
have  been  found  with  their  skins  curiously  scored  in  two 
parallel  lines,  especially  near  the  pudenda,  suggesting  the 
idea  that  they  are  liable  to  be  attacked  by  the  males. 

The  structure  of  these  teeth  is  not  less  peculiar  than 
their  general  form  ;  the  summit  of  the  tooth,  which  starts 


THE  TEETH  OF  CETACEA. 


339 


off  nearly  at  right  angles  to  the  shaft  (and  so,  the  shaft  being 
curved  over  the  top  of  the  upper  jaw,  comes  to  stand  nearly 
vertically)  consists  of  a  denticle  bluntly  pointed,  and 
mode  up  of  dentine  coated  with  enamel.  This  denticle  of 
triangular  shape  is  only  about  a  third  of  an  inch  in  length, 
and  in  the  adult  specimen  described  by  Professor  Sir  Wrn. 
Turner  had  the  enamel  coat  partially  worn  off. 

In  the  Challenger  Keports  (Zoology,  vol.  i.)  he  says,  “  In 
the  earlier  stage  their  structure  does  not  differ  materially 
from  the  ordinary  type  of  tooth  one  meets  with,  say  in  the 
human  or  carnivorous  jaw,  the  crown  being  formed  by  enamel, 
the  fang  by  cement,  whilst  the  great  body  of  the  tooth  con¬ 
sists  of  dentine,  in  which  is  a  marked  pulp  cavity,  com¬ 
municating  with  the  exterior  by  a  slit-like  aperture  at  the 
root  of  the  fang.  The  exceptional  character  these  teeth 
exhibit  in  the  erupted  condition  is  due  to  the  disappearance 
of  the  enamel  from  the  crown,  to  the  cessation  in  the  de¬ 
velopment  of  the  ordinary  dentine,  to  the  excessive  formation 
of  osteodentine,  of  modified  vasodentine,  and  of  cement,  by 
means  of  which  the  pulp  cavity  becomes  almost  obliterated, 
and  the  fang  assumes  dimensions  which,  in  the  case  of 
Mesoplodon  Layardii,  lead  to  the  production  of  a  tooth  having 
the  very  remarkable  form  and  relation  to  the  beak  which  I 
have  described.” 

As  may  be  gathered  from  the  above,  the  development  of 
the  tooth  starts  by  the  formation  of  the  denticle,  which  is 
of  an  ordinary  structure  ;  the  enamel  however  soon  ceases 
to  be  formed,  and  but  very  little  further  down,  so  does  the 
true  dentine,  not  however  before  cementum  has  begun  to  be 
formed  upon  its  exterior  (see  c  in  fig.  on  next  page).  Then 
there  comes  an  abrupt  change  in  direction,  and  in  the 
place  of  true  dentine  we  find  a  coarser  textured  tissue  which 
i  contains  large  vascular  canals. 

This  Professor  Turner  and  Professor  Lankester  regard  as 
la  vasodentine,  seeing  that  it  is  in  all  probability  a  product 

z  2 


340 


A  MANUAL  OF  DENTAL  ANATOMY. 


of  the  dentine  pulp.  Of  this  the  great  mass  of  the  tooth 
consists,  but  it  has  throughout  its  length  an  investment  of 
cementum  of  an  ordinary  type,  which  forms  a  complete 
exterior  layer  laminated,  full  of  lacuna?,  and  for  the  most 
part  devoid  of  Haversian  canals. 

Immediately  beneath  this  layer  there  is,  if  the  distinction 


Fig.  142  (*). 


be  not  exaggerated  in  the  drawing,  a  definite  stratum  of 
tissue  of  material  thickness  w7hich  is  characterised  by  an 
abundance  of  vascular  canals  arranged  perpendicularly  to 
the  surface  ( a  in  fig.  142),  which  is  regarded  by  Professor 
Turner  as  belonging  to  the  dentine  group  of  tissue,  i.e.  as 
being  a  vasodentine.  But  there  is  this  difficulty  in  accept¬ 
ing  this  view,  viz.,  that  near  to  the  denticle  it  is  seen  to  lie 
distinctly  outside  the  true  fine-tubed  dentine  (see  fig.  142) 
which  it  overlaps  to  a  considerable  extent  ;  now  if  this 
tissue  was  formed  by  the  dentine  pulp  we  have  the  anomaly 
of  a  pulp  first  forming  a  very  vascular  vasodentine,  then 
changing  to  forming  a  fine  tubed  normal  dentine  (which  is 

f1)  Upper  part  of  tooth  of  Mesoplodon,  after  Professor  Sir  W.  Turner. 
a,  Tissue  of  doubtful  origin,  permeated  by  vascular  canals  ;  c,  cementum  ; 
d,  dentine  ;  e,  enamel  ;  v,  vasodentine. 


THE  TEETH  OF  CETACEA. 


341 


exactly  the  reverse  of  what  is  met  with  in  other  creatures  in 
which  the  pulp  forms  these  two  structures),  and  finally  re¬ 
verting  to  the  building  up  of  a  vasodentine. 

Judging  by  analogy  this  seems  so  improbable  that  in  the 
absence  of  more  positive  knowledge  and  simply  judging  from 
the  figure,  I  should  be  inclined  to  refer  this  layer  to  the 
cementum.  Lower  down  in  the  shaft  of  the  tooth  anastomoses 
take  place  between  the  tubes  of  this  layer  and  those  of  the 
unquestionable  pulp  products,  but  anastomoses  between 
dentine  tubes  and  enamel  tubes,  and  between  dentine  tubes 
and  cement  lacunae  are  of  common  occurrence  in  many 
animals,  so  that  this  communication  does  not  prove  anything 
as  to  their  respective  origin. 

However  Professor  Lankester  lays  stress  upon  the  globular 
botyroidal  structure  of  this  layer,  which  he  states  shades 
oft1  into  the  fine  tubed  dentine,  so  that  it  may  perhaps  be 
regarded  as  an  excessive  development  of  the  globular  layer  of 
dentine,  rather  than  as  a  vasodentine.  In  reconciliation  of 
the  discrepancy  between  the  two  descriptions,  it  is  suggested 
by  Professor  Turner  that  the  vascular  canals  seen  by  him  in 
this  layer  may  have  become  obliterated  in  the  presumably 
much  older  specimen  described  by  Professor  Lankester. 

The  central  pulp  cavity  becomes  reduced  to  the  merest 
traces,  so  that  the  completed  tooth  is  almost  solid. 

In  the  Narwal  (Monodon  monoceros)  two  teeth  alone  per¬ 
sist,  and  these  are  in  the  upper  jaw.  In  the  female  the 
dental  germs  become  calcified,  and  attain  to  a  length  of 
about  eight  inches,  but  they  remain  enclosed  within  the 
substance  of  the  bone,  and  their  pulp  cavities  speedily  fill 
up.  In  the  male,  one  tusk  (in  some  very  rare  instances 
both)  continues  to  grow  from  a  persistent  pulp  till  it 
attains  to  a  length  of  ten  or  twelve  feet,  and  a  diameter  of 
three  or  four  inches  at  its  base.  This  tusk  (the  left)  is 
quite  straight,  but  is  marked  by  spiral  grooves,  winding 
from  right  to  left.  It  is  curious  that  in  one  of  the  speci- 


342 


A  MANUAL  OF  DENTAL  ANATOMY. 


mens,  in  which  the  two  tusks  had  attained  to  equal  and 
considerable  length,  the  spirals  on  the  two  wound  in  the 
same  direction  ;  that  is  to  say,  as  regards  the  sides  of  the 
head,  the  spirals  were  not  symmetrical  with  one  another. 

The  tusk  of  the  male  narwal  may  fairly  be  assumed  to 
serve  as  a  sexual  weapon,  but  little  is  known  of  the  habits 
of  the  animal. 

Professor  Sir  Wm.  Turner  has  lately  noted  the  occur¬ 
rence  of  two  stunted  incisor  rudiments  in  a  foetal  narwal : 
these  obviously  represent  a  second  pair  of  incisors,  and  attain 
to  a  length  of  half  an  inch,  but  are  irregular  in  form  ;  they 
are  situated  a  little  behind  the  pair  of  teeth  which  attain  to 
more  considerable  dimensions.  All  trace  of  this  second  pair 
of  incisors  is  lost  in  adult  skulls. 

The  whalebone  whales  are,  in  the  adult  condition,  des¬ 
titute  of  teeth,  but  prior  to  birth  the  margins  of  both  upper 
and  lower  jaws  are  covered  with  a  series  of  nearly  globular 
rudimentary  teeth,  which  become  calcified,  but  are  speedily 
shed,  or,  rather,  absorbed. 

The  foetal  teeth  of  the  Balsenoptera  rostrata  have  been 
carefully  described  by  M.  Julin  (. Archives  de  Biologie ,  1880), 
the  Balcenopteridce  having  been  previously  supposed  to  be 
without  rudimentary  teeth.  The  ramus  contained  41  tooth 
germs,  each  furnished  with  an  enamel  organ  and  dentine 
bulb,  with  a  slight  capsule ;  these  were  lodged  in  a  con  • 
tinuous  groove  in  the  bone  above  the  vessels,  thus  re¬ 
calling  the  condition  of  the  parts  in  a  human  embryo  at  a 
certain  stage.  A  very  small  amount  of  calcification  takes 
place,  a  mere  film  of  dentine  being  formed  upon  the  dentine 
bulb.  But  what  is  very  remarkable  is  that  the  dentine  bulbs 
are  simple  near  the  front,  bifid  in  the  middle,  and  trifid  at 
the  back  of  the  mouth ;  in  other  words,  these  tooth-germs 
would  go  to  form  lieterodont  teeth,  not  unlike  those  of  some 
seals,  or  of  Squalodon.  Hence  it  has  been  suggested  that 
the  whale  may  be  descended  from  some  such  ancestral  form. 


THE  TEETH  OF  CETACEA. 


343 


From  the  upper  jaw  of  an  adult  whalebone  whale  there 
hang  down  a  series  of  plates  of  baleen,  placed  transversely  to 
the  axis  of  the  mouth,  but  not  exactly  at  right  angles  to  it. 


Fig.  143  O). 


The  principal  plates  do  not  extend  across  the  whole  width  of 
the  palate,  but  its  median  portion  is  occupied  by  subsidiary 
smaller  plates.  The  whalebone  plates  are  frayed  out  at  their 
edges  and  collectively  form  a  concave  roof  to  the  mouth, 

I1)  Cranium  of  Xarwal  (Monodon  monoceros).  a.  Stunted  tooth,  with 
its  basal  pulp-cavity  obliterated.  b.  Long  tusk.  The  small  figure, 
giving  the  whole  length  of  the  tusk,  shows  the  proportion  which  it  bears 
to  the  rest  of  the  skull. 


344 


A  MANUAL  OF  DENTAL  ANATOMY. 


against  which  the  large  tongue  fits,  so  as  to  sweep  from  the 
fringes  whatever  they  may  have  entangled.  The  whale  in 
feeding  takes  in  enormous  mouthfuls  of  water  containing 
small  marine  mollusca,  this  is  strained  through  the  baleen 
plates,  which  retain  the  Pteropods  and  other  small  creatures, 
while  the  wTater  is  expelled.  Then  the  tongue  sweeps  the 
entangled  food  from  the  fringe  of  the  baleen  plates,  and  it 
is  swallowed.  Each  plate  consists  of  two  dense  but  rather 
brittle  laminae,  which  enclose  between  them  a  tissue 
composed  of  bodies  analogous  to  coarse  hairs.  By  the  pro¬ 
cess  of  wrear  the  brittle  containing  laminae  break  away, 
leaving  projecting  from  the  edge  the  more  elastic  central 
tissue  in  the  form  of  stiff  hairs. 

Each  plate  is  developed  from  a  vascular  persistent  pulp, 
which  sends  out  an  immense  number  of  exceedingly  long 
thread-like  processes,  which  penetrate  far  into  the  hard 
substance  of  the  plate.  Each  hair-like  fibre  has  within  its 
base  a  vascular  filament  or  papillae  :  in  fact,  each  fibre  is 
nothing  more  than  an  accumulation  of  epidermic  cells,  con¬ 
centrically  arranged  around  a  vascular  papilla,  the  latter 
being  enormously  elongated.  The  baleen  plate  is  composed 
mainly  of  these  fibres,  which  constitute  the  hairs  of  its  frayed- 
out  edge,  but  in  addition  to  this  there  are  layers  of  flat  cells 
binding  the  whole  together,  and  constituting  the  outer  or 
lamellar  portion.  As  has  been  pointed  out  by  Prof.  Sir  Wm. 
Turner  (Proc.  Boy.  Soc.  Edinburgh,  1870),  the  whalebone 
matrix  having  been  produced  by  the  cornification  of  the 
epithelial  coverings  of  its  various  groups  of  papillae,  is  an 
epithelial  or  epiblastic  structure,  and  morphologically  corre¬ 
sponds  not  with  the  dentine,  but  with  the  enamel  of  a  tooth. 

The  whole  whalebone  plate  and  the  vascular  ridges  and 
papillae  which  form  it  may  be  compared  to  the  strong  ridges 
upon  the  palates  of  certain  Herbivora,  an  analogy  which  is 
strengthened  by  the  study  of  the  mouth  of  young  whales 
prior  to  the  cornification  of  the  whalebone. 


THE  TEETH  OF  SI  RENTA. 


345 


THE  TEETH  OF  SIRENIA. 

More  nearly  connected  with  the  Ungulata  than  with  any 
other  order,  but  still  rather  widely  removed  from  them,  stands 
the  limited  order  of  Sirenia,  aquatic  mammals  formerly 
termed  Herbivorous  Cetacea,  a  term  rather  objectionable, 
as  they  are  not  very  nearly  allied  to  the  true  Cetacea. 

The  order  is  now  represented  by  two  genera  only,  the 
Dugongs  (Halicore)  and  the  Manatees  (Manatus),  but  a 
third  genus  (Rhytina)  has  only  become  extinct  within  about 
a  century.  Their  teeth,  and  other  points  in  their  organiza¬ 
tion  indicate  that  they  are  more  nearly  allied  to  the  Ungu¬ 
lata  than  to  any  other  group,  though  their  peculiarities  are 
such  as  to  elevate  them  to  the  rank  of  a  distinct  order.  They 
are  of  large  size,  and  frequent  shallow  water,  such  as  the 
mouths  of  great  rivers,  their  food  consisting  of  sea-wreed 
and  aquatic  plants.  Their  incisors  and  molars  when  both 
are  present  are  widely  separated,  and  the  former  vary  from 
being  quite  rudimentary  to  forming  formidable  tusks. 

The  dentition  of  the  Dugong  is  in  several  respects  a  very 
interesting  one  :  the  front  part  of  the  upper  jaw,  consisting 
in  the  main  of  the  intermaxillary  bones,  bends  abruptly 
downwards,  forming  an  angle  with  the  rest  of  the  jaw. 
This  deflected  end  of  the  jaw  carries  two  tusks,  of  each  of 
which  the  greater  part  is  buried  within  the  alveolus.  The 
tusk  has  an  investment  of  enamel  over  its  front  and  sides, 
but  on  the  posterior  surface  of  cementum  only,  so  that  in 
the  disposition  of  the  three  structures  it  recalls  the  charac¬ 
teristics  of  a  Rodent  incisor,  like  which  it  is  worn  away 
obliquely  so  as  to  keep  a  constantly  sharp  edge,  and  like 
which  it  grows  from  a  persistent  pulp. 

In  the  female,  the  tusks  (incisors)  do  not  project  from  the 
gum,  their  pulp  cavities  are  closed,  and  the  investment  of 
enamel  is  complete  over  the  top  of  the  tooth. 

The  sloping  surface  of  the  upper  jaw  is  opposed  by  the 


346 


A  MANUAL  OF  DENTAL  ANATOMY. 


region  of  the  symphysis  of  the  lower  jaw,  which  is  of  un¬ 
usual  depth.  In  this  deflected  part  of  the  lower  jaw  there 
are  eight,  or  ten  (four  or  five  on  each  side)  shallow  and 
rather  irregularly-shaped  sockets,  in  which  curved  distorted 


Fig.  144  (1). 


teeth  may  be  found  in  a  fresh  specimen,  but  it  must  not 
be  from  too  aged  an  animal,  as  they  eventually  become  eaten 
away  by  a  process  of  absorption. 

These  abortive  teeth  are  excellent  examples  of  rudi¬ 
mentary  teeth,  as  not  only  are  they  stunted,  and  even 
ultimately  removed  by  absorption,  but  they  are  actually 
covered  in  by  a  dense  horny  plate  which  clothes  this  part 
of  the  jaw,  and  so  are  absolutely  functionless. 


(  )  Side  view  of  cranium  and  lower  jaw  of  a  Dugong  (Halicore  Indicus). 
From  a  specimen  in  the  Museum  of  the  Royal  College  of  Surgeons.  The 
surface  of  the  deflected  portion  of  the  lower  jaw,  with  its  sockets  for 
rudimentary  teeth,  shown  both  in  front  and  in  profile  view,  is  indicated  by 
the  letter  a;  the  corresponding  surface  of  the  upper  jaw  by  the  letter  b. 


THE  TEETH  OF  S TRENT  A. 


347 


These  horny  plates,  in  their  structure  analogous  to  whale¬ 
bone,  are  possessed  also  by  the  Manatee  and  Bhytina  ;  on 
the  free  surface  they  are  beset  with  stiff  bristles,  and  are 
throughout  built  up  of  hair-like  bodies  welded  together  by 
epithelium. 

Behind  the  region  covered  in  by  the  horny  plates,  the 
Dugong  has  five  molar  teeth  on  each  side,  of  simple  form, 
like  those  of  the  Edentata,  and  consisting  of  dentine  and 
cementum  only. 

By  the  time  the  last  molar  is  ready  to  come  into  place, 
the  first  of  the  series  is  being  removed  by  absorption  of  its 
root  and  of  its  socket.  In  aged  specimens  only  two  molars 
remain  on  each  side  of  the  jaws.  Before  they  are  worn  they 
have  tuberculated  crowns  and  they  are  of  semi-persistent 
growth. 

The  Dugong  is  also  peculiar  as  having  a  single  deciduous 
tooth  :  namely,  a  predecessor  to  the  incisive  tusks  ;  but  it 
has  been  doubted  whether  it  be  not  rather  a  rudimentary 
incisor  than  a  milk  tooth. 

The  molar  teeth  of  thfi  Manatee  are  much  more  nume¬ 
rous  and  more  complex  in  form,  and  they  approach  to  the 
configuration  of  the  teeth  of  the  Tapir  very  closely. 

The  Manatee  has  as  many  as  forty-four  molars,  which 
are  not,  however,  all  in  place  at  one  time,  the  anterior  ones 
being  shed  before  the  posterior  are  come  into  place  ;  no 
vertical  succession  is  known  to  take  place  amongst  them. 

2 

The  Manatee  has  i  - ,  but  they  are  rudimentary,  and  are 

buried  in  the  horny  plates  which  should  occupy  the  front  of 
the  mouth.  Gervais  (Hist.  Nat.  des  Mammiferes,  vol.  ii.)  gives 
a  larger  number  of  rudimentary  teeth,  as  many  as  twelve. 

It  has  been  mentioned  that  the  teeth  of  the  Manatee  are 
tapiroid  in  external  form ;  they  also  possess  peculiarities  in 
minute  structure,  which  are  unusual  in  mammalian  teeth,  but 
which  are  common  to  them  and  to  the  Tapirs.  In  examining 


348 


A  MANUAL  OF  DENTAL  ANATOMY. 


some  teeth,  I  found  that  the  dentine,  to  all  intents  and  pur¬ 
poses  of  the  hard  unvascular  variety,  was  permeated  by  a 
system  of  larger,  or  “vascular”  canals,  which  were  arranged 
with  much  regularity,  and  passed  out  from  the  pulp  cavity  to 
the  periphery  of  the  dentine,  where  they  communicated  with 
one  another.  The  dentinal  tubes  did  not  radiate  from  these 
vascular  canals  ;  they,  so  to  speak,  take  no  notice  of  them,  so 
that  there  is  an  ordinary  unvascular  dentine  with  a  system 
of  capillary-conveying  channels  inside  it.  It  is  interesting 
to  find  that  the  primd  facie  external  resemblance  of  the 
teeth  to  those  of  the  Tapir  is  fully  borne  out  by  minute  his¬ 
tological  structure,  and  it  certainly  suggests  that  the  resem¬ 
blance  is  not  accidental,  but  has  some  deeper  significance. 

The  enamel  of  the  Manatee  is  also  somewhat  remarkable 
for  the  absolute  straightness  of  its  enamel  prisms  in  many 
parts  of  the  tooth. 

The  molar  teeth  of  the  Dugong  consist  of  a  central  axis 
of  vaso-dentine,  a  much  larger  mass  of  ordinary  unvascular 
dentine,  and  a  thick  layer  of  cementum,  but  they  do  not 
share  the  peculiarities  of  the  Manatee’s  tooth. 

The  Manatee  has  a  curious  manner  of  feeding  •  the  halves 
of  the  upper  lip,  deeply  cleft  in  the  middle,  are  beset  with 
short  stiff  bristles,  and  are  used  to  tuck  things  into  the  mouth ; 
when  these  fail  the  flappers  are  raised  and  used  to  assist. 

The  extinct  Rhytina,  a  little  more  than  a  century  ago 
abundant  in  Behring’s  Straits,  was  altogether  without  teeth, 
but  was  furnished  with  dense,  strongly-ridged,  horny  plates. 
Sirenia  were  abundant  in  Miocene  and  Pliocene  seas ;  the 
Halitherium  had  molars  somewhat  like  the  Manatee,  but 
had  tusk-like  incisors  in  the  upper  jaw.  No  vertical  suc¬ 
cession  is  known  to  take  place  in  any  Sirenian,  though  the 
anterior  molars  of  Halitherium  were  deciduous. 


CHAPTER  X. 


THE  TEETH  OF  INSECTIVORA  AND  CHIROPTERA. 

# 

The  Insectivora  form  rather  a  heterogeneous  order  of 
Mammals,  and  embrace  very  various  forms.  All  of  them  are 
of  rather  small  size,  and  some  are  very  small  indeed.  Their 
diet  consists  for  the  most  part  of  insects,  and  their  teeth  are 
generally  adapted  for  this  by  being  furnished  with  many 
points.  The  best  known  animals  in  the  order  are  the 
Hedgehogs,  the  Shrews,  the  Moles,  and  the  Macroscelida> 
(Elephant  mice)  ;  to  these  is  to  be  added  the  Galeopithecus, 
or  “  Flying  Lemur.”  Insectivora  are  more  abundant  in 
Africa,  Asia,  and  South  America  than  in  Europe.  The 
Shrews  approximate  in  some  measure  towards  the  Rodents, 
and  the  Tupaia  is  very  lemurine  in  its  characters. 

They  all  have  small  brains,  and  long  faces.  The  Insec¬ 
tivora  are  ancient  and  in  some  respects  rather  generalised 
mammals,  so  that  they  may  be  supposed  not  to  have  diverged 
far  from  the  parent  forms  of  other  mammalia.  Prof.  Cope 
has  described  a  good  many  genera  which  have  been  found  in 
American  Eocene  Strata,  and  some  of  these,  e.g .,  Mesonyx, 
had  teeth  differentiated  into  incisors,  large  canines,  pre- 
molars  and  molars,  but  these  last  two  were  of  simple  form, 
being  in  the  lower  jaw  cones,  with  slight  anterior  and 
posterior  cusps  added  by  elevations  of  the  cingulum. 

The  upper  molars  had  crowns  which  were  rendered 
triangular  upon  the  grinding  surface  by  the  development  of 
an  internal  cusp. 

Its  dental  formula  was 


350 


A  MANUAL  OF  DENTAL  ANATOMY. 


.3  1  4  3 

1  2  C  I  Pm  4  m  3  ‘ 

Of  the  teeth  of  Insectivora  generally  it  may  be  said  that 
it  would  not  be  difficult  to  imagine  how  the  teeth  of  all 
other  Diphyodont  Mammals  might  be  evolved  from  them, 
whilst  Prof.  Cope  (Proc.  Acad.  Nat.  Sc.  Philadelphia,  1883, 
and  passim;  see  also  D.  Wortman,  Americ.  System  Dental 
Surgery,  Teeth  of  Yertebrata)  gives  an  admirable  series  of 
extinct  genera  in  which  the  molar  patterns  become  more 
complex,  and  approximate  on  the  one  hand  to  the  sectorial 
teeth  of  Carnivora,  and  on  the  other  to  the  bristling  cusps 
of  modern  Insectivora. 

• 

Galeopithecus  stands  alone  :  it  wras  formerly,  and  is  indeed 
sometimes  even  now,  placed  with  the  Lemurs  ;  but  it  has 
much  more  in  common  with  Insectivora.  The  teeth  are 
somewhat  anomalous,  the  lower  incisors  being  divided  by  a 
number  of  vertical  divisions  running  down  through  a  great 
part  of  the  length  of  the  crowns,  so  that  they  can  be 
compared  to  combs,  or  to  hands  with  the  fingers  slightly 
separated.  What  the  purpose  served  by  these  combdike 
teeth  maybe  remains  uncertain  :  no  other  animal  has  similar 
teeth.  Galeopithecus  has  a  well  developed  milk  dentition, 
the  milk  teeth  being  very  similar  to  their  successors. 

The  dental  formula  is 

.21  23 

1  3  °  I  Pm  2  m  3  ’ 

and  the  second  upper  incisor  and  the  canine  are  two-rooted. 

Excluding  Galeopithecus,  the  others  are  divided  into  two 
groups  by  the  patterns  of  the  molars  ;  the  majority  present 
a  W -pattern  (Tupaia,  Macroscelis,  Erinaceus,  Sorex,  Talpa), 
whilst  the  other  group  have  narrower  molars  with  a  V- 
pattern  (Potaomgale,  Centetes,  Chrysochloris). 

The  W-pattern  characterising  the  molars  of  Insectivora  is 

# 

well  exemplified  in  the  molar  of  Urotriclius. 


THE  TEETH  OF  INSECT  IVOR  A. 


351 


In  this  tooth,  as  has  been  clearly  shown  by  Prof.  Mivart 
(Osteology  of  Insectivora,  Journ.  of  Anat.,  1868),  the  four 
cusps  of  the  typical  teeth  (a,  b,  c,  d)  have  been  added  to 
by  the  elevation  of  the  cingulum  into  three  or  four  external, 
and  one  internal  cusp,  making  up  the  total  number  to  nine. 
Thus  it  is  that  the  molars  of  this  order  often  fairly  bristle 
with  cusps. 

In  the  Mole  the  number  of  cusps  is  diminished  by  the 
coalescence  of  b  and  d  into  a  ridge,  and  the  disappearance  of 

Fig.  145  (P. 


AFC 


the  inner  cusp  of  the  cingulum,  while  the  simplification  is 
carried  yet  further  in  the  Cape  Mole  (c  in  Fig.  145). 

The  common  English  Hedgehog  (Erinaceus)  has  the  dental 
formula 

•  3  o  4  3 

i  -  c  _  pm  —  m  -  . 

2  o  F  3  3 

In  the  upper  jaw  there  is  a  wide  interval  between  the 
first  pair  of  incisors,  which  are  much  the  largest,  and  are 
caniniform  in  shape.  The  next  two  teeth  (incisors)  are 
quite  small,  and  resemble  premolars  in  their  form.  The 
next  tooth  has  two  roots,  and  a  crown  with  one  cusp,  and  is 

O  Upper  molar  teeth  of  (A)  Urotrichus  ;  (B)  Mole  ;  and  (C)  Chryso- 
chloris.  The  four  principal  cusps  are  lettered  a,  b,  c,  d,  in  each  of  the 
figures.  In  A  the  cingulum  lias  been  elevated  so  as  to  form  four  additional 
cusps  on  the  exterior  of  the  tooth,  and  one  additional  cusp  on  the  interior. 
B  and  C.  show  the  fusion  of  certain  of  these  cusps,  and  the  consequent 
diminution  in  their  number.  (From  Mivart. ) 


352 


A  MANUAL  OF  DENTAL  ANATOMY. 


also  like  tlie  premolars  behind  it.  This  tooth,  the  root 
of  which  shows  indications  of  division,  is  sometimes  called 
a  canine,  because  it  comes  next  behind  the  intermaxillary 
suture  ;  behind  this  come  two  small  premolars. 

The  fourth  upper  premolar  is  totally  different  in  size  and 
form  from  the  third  :  its  crown  is  large,  squarish,  and 
furnished  with  four  cusps,  of  which  the  antero-external  one 
is  far  the  longest  and  sharpest. 

The  first  upper  true  molar  has  a  square  crown,  upon 
which  are  four  sharp  cusps  :  it  is  implanted  by  four  roots. 

Fig.  146  (i). 


The  second  true  molar  is  also  square,  quadricuspid,  and 
has  four  roots  ;  but  it  is  much  smaller  than  the  first,  while 
the  third  upper  true  molar  is  quite  a  small,  compressed, 
double-rooted  tooth,  with  a  thin-edged  crown. 

In  the  lower  jaw  the  first  incisors,  less  widely  separated 
than  the  upper,  are  also  the  largest ;  then  follows  another 
tooth  termed  incisor,  on  account  of  its  relation  to  the  upper 
incisors  when  the  mouth  is  closed.  The  third  tooth  is 
much  larger,  and  of  peculiar  form.  The  fourth  tooth  from 
the  front  is  a  small  single  tooth,  like  the  third,  but  upon  a 
smaller  scale.  Next  behind  it,  comes  a  tooth  which  is  very 


i1)  Upper  and  lower  teeth  of  the  Hedgehog. 


THE  TEETH  OF  INSEOTIVORA. 


353 


much  larger,  and  its  crown  carries  two  principal  cusps  with 
a  small  subsidiary  cusp.  The  next  tooth  (first  true  molar) 
has  an  oblong  crown  beset  with  five  sharp  cusps,  of  which 
four  are  arranged  at  the  corners  of  a  square,  while  the  fifth, 
obviously  an  elevation  of  the  cingulum,  lies  a  little  in  front 
and  towards  the  inside  of  the  tooth.  In  the  second  true 
molar  the  fifth  cusp  is  but  little  indicated,  while  the  last 
true  molar  is  a  dwarfed  tooth  with  but  one  cusp.  Several 
dental  formulae  have  been  assigned  to  the  Hedgehog :  there 
is  little  room  for  difference  of  opinion  as  to  the  nomen¬ 
clature  of  its  upper  teeth :  though  some  authors  {e.g., 
Professor  Mivart)  prefer  to  call  the  first  premolar  a  canine. 
But  in  the  lower  jaw  some  authors  give  i  ^  c  t  pm 

— J  X  4mJ 


others  i  —  c  —  pm  — ,  and  others  again,  i  — 
3  0  1  2  °  5  2 


Pm  3 


The 


last  given  seems  the  least  artificial,  and  corresponds  best 
with  the  relations  between  the  upper  and  lower  teeth  when 
the  mouth  is  closed. 

Rousseau  describes  the  existence  of  twenty-four  milk 

.34 

teeth,  which  he  classifies  thus  :  (i  —  dm  -) ;  that  is  to  say, 

all  the  teeth  in  front  of  the  true  molars  had  deciduous  pre¬ 
decessors,  but  his  grouping  of  them  into  incisors  and  molars 
is  quite  arbitrary. 

The  milk  teeth  are  not  shed  and  replaced  until  the 
animal  has  attained  to  almost  its  full  dimensions,  and  all 
three  true  molars  are  in  place. 

The  teeth  of  the  Hedgehog  fairly  represent  some  of  the 
features  of  Insectivorous  dentitions,  for  the  forcep-like  in¬ 
cisors,  the  stunted  or  non-developed  canines,  and  the  molars 
bristling  with  pointed  cusps,  are  common  to  very  many  of 
the  order. 

The  Shrews  have  numerous  sharply-pointed  teeth,  the 
points  interdigitating  and  fitting  very  closely  together 


354 


A  MANUAL  OF  DENTAL  ANATOMY. 


when  the  mouth  is  shut.  There  is  no  tooth  either  in  the 
upper  or  lower  jaw  which  is  so  elongated  as  to  deserve  the 
name  of  canine ;  but  between  the  incisors  and  the  true 
molars  are  several  small  teeth  which,  by  analogy,  are  called 
premolars.  The  true  molars  are  not  very  different  in 
pattern  from  those  of  the  mole  (B  in  Fig.  130),  and  present 
the  W  -contour  so  common  in  the  molars  of  Insectivora. 

The  most  marked  peculiarity  in  the  dentition  of  the 
Shrews  lies  in  the  form  of  their  incisors.  The  first  upper 
incisor  is  always  very  large  indeed :  it  looks  vertically 
downwards,  is  a  little  hooked,  and  has  a  notch,  and  a  second 
low  cusp  behind  the  principal  long  pointed  cusp.  The  tip 
of  the  lower  incisor  fits  into  this  notch.  The  lower  incisor 
is  also  very  large ;  it  lies  nearly  horizontally,  though  the 
point  is  bent  a  little  upwards.  Along  its  upper  edge  there 
are,  in  most  species,  three  or  four  small  cusps,  while  its 
lower  border  is  curiously  prolonged  outside  the  bone  of  the 
jaw,  so  as  to  in  some  measure  encase  this  latter.  The  lower 
incisor  is  at  least  one-third  as  long  as  the  whole  alveolar 
border.  The  incisor  teeth  of  the  Shrew  wrould  appear  to 
form  a  very  efficient  pair  of  pincers,  with  which  to  pick  up 
the  minute  creatures  on  which  it  feeds.  Of  the  milk  teeth 
of  Shrews  little  is  known :  they  are  said  to  be  absorbed 
before  birth,  but  accurate  observations  upon  them  are  much 
needed,  their  very  existence  being  doubtful. 

The  dentition  of  the  Mole  (Talpa)  has  been  the  subject  of 
much  controversy,  the  determination  of  its  canines,  &c., 
presenting  such  difficulty  that  no  less  than  five  different 
dental  formulae  have  been  assigned  to  it. 

In  the  front  of  the  upper  jaw  come  three  small  teeth,  the 
first  being  somewhat  the  largest,  which  are  well  within  the 
limits  of  the  intermaxillary  bone,  and  are  doubtless  incisors. 
But  the  next  tooth,  which  is  very  big,  also  appears  to  be 
implanted  in  the  intermaxillary  bone,  the  suture  passing 
across  its  socket  close  to  the  back  of  its  posterior  root. 


THE  TEETH  OF  INSECTIVORA.  355 


According  to  its  implantation  it  therefore  would  be  an 
incisor  (x)  but  it  is  very  unlike  an  incisor ;  and  it  is  two- 
rooted,  a  thing  anomalous  either  in  an  incisor  or  a  canine, 
though  found  in  the  canine  of  Gymnura,  which  is  beyond 
question  in  the  maxillary  bone. 

Next  come  three  minute  premolars,  and  a  fourth,  which 
is  much  larger  than  the  others  :  these  all  have  simple 

Fig.  147  (2). 


ciowns,  consisting  of  little  more  than  a  single  sharply- 
pointed  cusp. 

The  first  two  upper  molars  are  large  teeth  bristling  with 
cusps :  the  third  is  much  reduced  in  size  and  simplified 
in  pattern.  In  the  lower,  jaw  the  four  front  teeth  are  all 
small,  but  the  fourth  or  outermost  of  these  incisors  is  called 
by  some  writers  the  lower  canine,  because,  when  the  teeth 
are  closed,  it  passes  in  front  of  the  upper  caniniform  tooth. 

(x)  The  late  Mr.  Spence  Bate,  in  his  valuable  paper  on  the  milk  teeth 
of  the  mole,  says,  “  This  tooth  is  implanted  within  the  limits  of  the  pre¬ 
maxillary  bones,  the  suture  separating  them  from  the  maxillary,  passing 
through  the  posterior  portion  of  its  alveolus  :  thus  demonstrating  that  this 
deciduous  tooth  is  the  true  homologue  of  that  of  the  canine  in  the  mam¬ 
malian  type.”  Surely  it  would  go  to  prove  the  contrary,  if  accepted  as 
j  evidence  at  all  upon  this  point. 

(2)  Upper  and  lower  teeth  of  the  common  Mole.  The  functionless  milk 
teeth  (after  Spence  Bate)  are  placed  above  the  permanent  teeth  which 
displace  them. 


A  A  2 


356 


A  MANUAL  OF  DENTAL  ANATOMY. 


Nevertheless  the  tooth  which  does  the  work  of  a  canine  in 
the  lower  jaw  is  the  fifth  counting  from  the  front  :  this  is  a 
two-rooted  tooth,  and  conforms  so  closely  with  the  three 
teeth  behind  it  in  configuration,  that  it  is  obviously  only  one 
of  these  premolars  developed  to  a  greater  length  than  the 
others.  It  closes  behind  the  caniniform  upper  tooth,  so 
cannot  on  this  ground  be  called  a  canine  by  those  who 
attach  importance  to  the  term. 

The  remaining  three  premolars  are  rather  small  and 
single ;  the  true  molars  are  of  considerable  size,  and  their 
points  are  very  long  and  sharp. 

I  have  purposely  avoided  giving  any  dental  formula  for 
the  Mole  :  everything  turns  upon  the  value  which  we 
attach  to  the  term  canine ;  and  I  have  already  given  reasons 
for  attaching  but  little  homological  importance  to  its 
determination. 

The  late  Mr.  Spence  Bate’s  paper  (Trans.  Odontol.  Society, 
1867),  valuable  as  it  is  in  contributing  to  our  whole  know¬ 
ledge  of  the  milk  dentition  of  the  creature  does  not  finally 
determine  the  homologies  of  the  canine. 

In  a  Mole  3f  inches  long  he  found  eight  milk  teeth  on 
each  side  of  both  upper  and  lower  jaws,  as  is  indicated  in 
Fig.  147.  The  milk  incisors  were  about  one-twentieth  of 
an  inch  in  length,  and  one  two-hundredth  in  diameter,  and 
were  rudimentary  in  form,  consisting  of  long  thin  cylindrical 
tubes  surmounted  by  slightly  expanded  crowns.  All  the 
milk  teeth  were  of  this  simple  form,  save  only  the  last  in 
each  jaw,  which  presented  crowns  with  two  cusps,  and  had 
their  roots  to  some  little  extent  divided  into  two. 

At  the  time  when  these  teeth  are  present  the  intermaxil*  j 
lary  suture  is  very  distinct,  and  there  is  no  doubt  that  the 
fourth  upper  milk  tooth,  the  predecessor  of  the  caniniform 
tooth,  is  in  the  intermaxillary  bone. 

The  teeth  had  not  fairly  cut  the  gum,  and  the  advanced 
state  of  the  permanent  teeth  beneath  them  make  it  doubtful 


THE  TEETH  OF  CHIROPTERA. 


357 


whether  they  ever  do  become  erupted.  At  all  events,  they 
can  be  of  no  use. 

In  many  of  the  order  Insectivora  the  milk  dentition  is 
unknown,  but  we  have  exemplified  amongst  them  every 
grade  of  completeness  in  its  development.  Thus  in  the 
Hedgehog  and  Centetes  (an  allied  animal  from  Madagascar) 
the  milk  dentition  is  tolerably  complete,  while  in  the 
Shrews  it  has  all  but,  or  quite,  disappeared. 

The  teeth  of  Insectivora  are  remarkable  for  the  thickness 
of  their  enamel,  which  in  the  Shrews  is  to  some  extent 
penetrated  by  the  dentinal  tubes.  The  enamel  is  deeply 
coloured  in  some  Shrews,  the  pigment  being  actually  in  the 
substance  of  the  enamel,  and  not  in  any  distinct  layer. 


THE  TEETH  OF  CHIROPTERA. 


The  Bats,  sharply  distinguished  from  all  other  mammals 
by  the  possession  of  wings,  are  divided  into  two  groups, 
respectively  insectivorous  and  frugivorous. 

The  insectivorous  Bats,  by  far  the  most  numerous  section, 
are  for  the  most  part  possessed  of  small  incisors,  rather 
large  canines,  and  premolar  and  molar  teeth  which  bristle 
with  sharp  cusps,  and  generally  present  the  W-pattern.  In 
fact,  in  general  character,  their  teeth  resemble  those  of  the 
Insectivora,  but  the  dental  formula  never  exceeds — 


.21  33 

l  -  c  —  pm  -  m 

3  1  1  3  3 


i 

\ 

i 


The  incisors  are  sometimes  reduced  in  number,  and 
spaces  left  between  them ;  and  some,  as  for  example,  the 
Vampire  (Desmodus)  have  teeth  specially  modified  to  accord 
with  their  blood-sucking  habits. 

This  Bat  has  only  one  permanent  incisor  on  each  side,  and 
this  is  a  large  but  thin  and  sharp-edged  tooth,  with  which 


358 


A  MANUAL  OF  DENTAL  ANATOMY. 


the  wound  is  made  ;  the  lower  incisors  are  small  teeth  with 
feebly  notched  edges.  The  canines  are  large,  and  the  molar 


Fig  148  l1) 


series,  which  is  not  required  in  an  animal  existing  upon 
blood,  is  stunted.  The  molar  teeth  are,  however,  sharp, 
though  small,  and  there  is  no  marked  distinction  into 
molars  and  premolars  :  the  dental  formula  is — 

.10  201 

i  -  c  -  pm  -  m  -  or— . 

2  0  1  3  0  1 

The  frugivorous  bats  (of  which  the  Pteropus,  or  flying 
fox,  is  an  example)  have  much  larger  muzzles,  and  the  molar 
teeth  are  set  with  intervals  between  them. 

2  1  2  3 

The  dental  formula  is  i  —  c  -  pm  —  m  but  in  some  the 

2  1  1  3  3 

molar  series  is  reduced  below  this  number. 

The  incisors  are  small,  and  the  canines  rather  large. 

Both  molars  and  premolars  are  of  somewhat  simple  form, 
being  long,  and  compressed  from  side  to  side.  The  outer 
borders  of  the  crown  of  the  molars  are  elevated  into  distinct 
but  not  exceedingly  sharp  cusps,  which  become  worn  down 
by  use. 

(l)  Skull  of  Desmodus,  showing  milk  teeth. 


THE  TEETH  OF  CH IR  OPT  ERA . 


359 


The  insectivorous  character  of  the  presence  of  many 
sharp  cusps  upon  the  teeth  is  not  to  be  found  in  any  of  the 
frugivorous  bats.  All  the  Pteropi  have  deciduous  canines, 
and  four  deciduous  molars,  of  simple  pointed  form,  but  the 
number  of  deciduous  incisors  is  very  variable. 

The  milk  dentition  of  bats  has  been  very  carefully  and 
thoroughly  investigated  by  Leche  (Lund’s  Universit.  Ars- 
skrift,  Tom.  XII.  and  XIV.,  1878),  and  at  the  present  the 
Megadermata  are  the  only  family  in  which  the  milk  teeth 
are  unknown.  The  milk  teeth  are  not  of  much  functional 
importance,  as  they  are  shed  soon  after,  if  not  absorbed 
before,  birth,  and  they  are  not  therefore  implanted  in  very 
definite  sockets. 

In  their  slight  cylindrical  elongated  roots,  surmounted  by 
expanded  crowns,  these  milk  teeth  often  recall  those  of  the 
Mole. 

Sometimes  the  milk  teeth  are  to  be  found  even  after  the 
permanent  teeth  are  in  situ;  in  other  instances,  as  for 
example  the  deciduous  molars  of  Molossus,  they  never  cut 
the  gum.  The  milk  dentition  of  the  Vampire  (Desmodus)  ( 1 ) 
appears  to  consist  of  incisors  only,  or  of  incisors  and 
canines ;  though  the  absence  of  observed  molars  may  be 
due  to  the  fact  that  they  are,  as  in  Molossus,  shed  very 
early. 

It  has,  near  to  the  front  of  the  upper  jaw,  six  teeth,  each 
of  which  is  very  long  and  slender,  and  has  a  strongly  hooked 
point :  it  has  been  suggested  that  these  feeble  hooked  teeth 
may  assist  it  in  holding  on  to  the  mother. 

In  general  terms  it  may  be  said  that  the  milk  teeth  of  the 
majority  of  Chiroptera  do  not  at  all  resemble  their  per¬ 
manent  successors. 

(b  In  a  skull  of  Desmodus,  in  tlie  possession  of  Mr.  It.  F.  Tomes,  tlie 
third  milk  tooth  appears  to  correspond  in  position  to  the  permanent 
canine ;  the  same  is  the  case  in  the  specimen  figured  by  Messrs.  Gervais 
and  Castelmain  (Exped.  dans  les  part.  cent.  d’Amerique  du  Sud). 


360 


A  MANUAL  OF  DENTAL  ANATOMY. 


An  anomalous  dentition  has  been  found  in  a  New  Guinea 
Bat,  in  which  the  canines,  whilst  having  a  long  principal 
cusp,  are  rendered  multi-tuberculate  by  other  cusps  at  their 
base,  this  pattern  being  more  or  less  repeated  in  the  other 
teeth.  (Oldfield  Thomas,  Proc.  Zool.  Society,  1889.) 


THE  TEETH  OF  EODENTIA. 


The  animals  belonging  to  this  order,  which  is  sharply 
defined,  are  scattered  almost  all  over  the  world  ;  the  island 
of  Madagascar  is,  however,  remarkable  for  being  almost 
without  indigenous  Bodents,  as  is  the  case  also  with  Aus¬ 
tralia,  two  facts  which  are  of  no  small  interest  to  the 
student  of  odontology. 

For  in  each  of  these  areas,  out  of  the  creatures  which  are 
there  (in  the  one  Lemurs,  in  the  other  Marsupials),  there 
has  arisen  a  form  so  modified  as  to  mimic  and  take  the  place 
of  the  true  Rodents,  viz.,  the  Cheiromys  in  Madagascar,  and 
the  Wombat  in  Australia. 

The  species  of  Rodents  are  exceedingly  numerous,  and 
the  great  majority  of  them  are  of  small  size;  the  aquatic 
Capybara  is  far  the  largest  of  recent  Rodents. 

An  average  Rodent  dentition  would  be 


as  extremes  the  Hare  has 


1  -  c  —  pm  —  or  -  m  — 
10‘1  0  3 


.10  10  3 

l  c \  "nm  c\  v  yvv  • 


.2  0  3  3 

i  -  c  -  pm  -  m  — 

1  0  1  2  3 


and  Hydromys 


.  1  0 


0  2 


THE  TEETH  OF  RODENTIA. 


361 


In  general  features  the  dentitions  of  the  numerous 
species  comprising  this  order  are  very  uniform  ;  the  incisors, 
(save  in  the  hares  and  rabbits,  in  which  there  is  an  ac¬ 
cessory  small  pair  immediately  behind  the  large  ones)  are 
reduced  to  four  in  number,  are  of  very  large  size,  and  grow 
from  persistent  pulps.  The  jaws  for  some  little  distance 
behind  the  incisors  are  devoid  of  teeth,  while  beyond  the 
interval  the  back  teeth,  generally  not  more  than  four  in 
number,  are  arranged  in  lines  which  diverge  slightly  as  they 
pass  backward.  The  large  scalpriform,  or  chiseldike  incisors, 
extend  far  back  into  the  jaws,  and  are  much  curved,  the 


Fig.  149  (]). 


upper  incisors,  in  the  words  of  Professor  Owen,  forming  a 
larger  segment  of  a  smaller  circle  than  the  lower,  which  are 
less  curved.  The  length  and  curvature  of  these  incisors 
relieve  from  direct  pressure  their  growing  pulps,  which 
come  to  be  situated  far  back  in  the  jaw,  the  open  end  of  the 
lower  incisor,  for  example,  being  in  many  species  actually 
behind  the  last  of  the  molar  teeth.  The  nerve  going  to 
supply  the  persistent  pulps  is  of  very  large  size,  and,  owing 
to  the  open  end  of  the  tooth  having  formerly  occupied  a 
i 

(!)  Side  view  of  skull  of  a  Rodent,  giving  a  general  idea  of  the  denti¬ 
tion  of  the  order. 


362 


A  MANUAL  OF  DENTAL  ANATOMY. 


more  anterior  position  in  the  jaw,  runs  forward  beneath  the 
tooth,  and  then  bends  abruptly  backwards  to  reach  the 
tooth-pulp.  In  many  Rodents  the  enamel  of  the  front  of 
the  large  incisors  is  stained  of  a  deep  orange  colour ;  this 
colour  is  situated  in  the  substance  of  the  enamel  itself. 

The  scalpriform  incisors  terminate  by  cutting  edges,  the 
sharpness  of  which  is  constantly  maintained  by  the  peculiar 
disposition  of  the  tissues  of  the  tooth. 

The  investment  of  enamel,  instead  of  being  continued 
round  the  whole  circumference  of  the  tooth,  is  confined  to 
its  anterior  and  lateral  surfaces,  on  the  former  of  which  it  is 
thickest. 

It  is,  however,  stated  that  the  enamel  organ  is  continued 
round  the  roots,  so  that  the  connective  tissue  bundles  by 
which  attachment  to  the  cementum  is  made,  have  to  grow 
through  it  to  take  their  hold.  (v.  Brunn.) 

It  is  said  by  Hilgendorff  (Berlin  Akad.  d.  Wiss.  Monats- 
bericht,  1865),  that  the  incisors  of  hares  differ  from  those  of 
all  other  Rodents  in  having  enamel  all  round  them,  although 
it  is  very  thin  at  the  back.  I  have  not  been  able  to  satisfy 
myself  that  the  thin  clear  layer  at  the  back  of  the  tooth  is 
enamel,  and  am  disposed  to  regard  it  as  cementum,  the  more 
so  as  it  seems  to  be  continued  a  little  way  upon  the  enamel, 
and  in  very  young  teeth  the  large  cells  of  the  enamel  organ 
are  confined  to  the  anterior  surface.  Q) 

When  a  Rodent  incisor  has  been  exposed  to  wear,  the 
anterior  layer  of  enamel  is  left  projecting  beyond  the  level 
of  the  dentine,  and  this  arrangement  results  in  a  very  sharp 
edge  being  constantly  maintained.  The  dentine  also  is 
harder  near  to  the  front  of  the  tooth  than  towards  the  back 
of  the  tooth. 

A  thin  external  coat  of  cement  is  found  upon  the  back  of 
the  tooth,  but  is  not  continued  far  over  the  face  of  the 
enamel.  In  the  marsupial  w’ombat  this  layer  of  cement  is 

(b  Cf.  E.  Gr.  Betts,  Trans.  Odontological  Society,  May,  1884. 


THE  TEETH  OF  RODENT  I  A. 


363 


continued  over  the  whole  anterior  surface  of  the  scalpriform 
incisors. 

The  molar  teeth  are  not  very  numerous ;  the  mouse 


family  have 


usually 


the  porcupines  have  constantly 


4  6 

,  and  the  hares  -  ;  the 

4  5 


Australian  water-rat  (Hy- 


dromys)  is  altogether  exceptional  in  having  so  few  as 


2 

—  • 

2 


Observation  has  established  that  the  last  three  of  these 
teeth  are  always  true  molars,  and  that  when  there  are  more 
than  three,  the  rest  are  premolars,  and  have  had  deciduous 
predecessors. 

But  the  extent  to  which  the  milk  teeth  are  developed 
varies  much.  Mr.  Waterhouse  (Nat.  Hist,  of  Mammalia — 
Rodents,  p.  4),  has  found  the  milk  molar  still  in  place  in 
the  skull  of  a  half-grown  beaver,  while  in  the  hares  they 
are  shed  about  the  eighteenth  day  after  birth,  and  in  the 
guinea-pig  disappear  before  birth.  Deciduous  incisors  have 
not  been  found  in  any  of  the  group,  save  in  the  hares  and 
rabbits. 

In  the  hares  and  rabbits  there  are  four  incisors  in  the 
upper  jaw,  a  small  and  apparently  functionless  pair  being 
placed  close  behind  the  large  rodent  incisors ;  but  in  very 
young  specimens  there  are  six  incisors,  of  which  the  one  pair 
are  soon  lost. 

Prof.  Huxley  (Nature,  vol.  23,  p.  228)  has  recently  written 
that  “  the  deciduous  molars  and  the  posterior  deciduous 
upper  incisors  of  the  rabbit  have  been  long  known.  But  I 
have  recently  found  that  unborn  rabbits  possess,  in  addi¬ 
tion,  two  anterior  upper  and  two  lower  deciduous  incisors. 
Both  are  simple  conical  teeth,  the  sacs  of  which  are  merely 
embedded  in  the  gum.  The  upper  is  not  more  than  one- 
hundredth  of  an  inch  long,  the  lower  rather  larger.  It 
would  be  interesting  to  examine  foetal  guinea-pigs  in  rela¬ 
tion  to  this  point ;  at  present  they  are  known  to  possess 


364 


A  MANUAL  OF  DENTAL  ANATOMY. 


only  the  hindmost  deciduous  molars,  so  far  agreeing  with 
the  Marsupials/’ 

Hares  and  rabbits  have  six  milk  molars  in  the  upper  and 
four  in  the  lower  jaw,  which  come  into  use,  but  differ  from 
their  successors  in  forming  definite  roots  and  not  growing 
from  persistent  pulps. 

Other  Rodents,  such  as  the  rat,  which  has  only  three 
teeth  of  the  molar  series  on  each  side,  and  the  Australian 


Fig.  150  f1). 


water-rat  (Hydromys)  have  no  known  milk  teeth,  and  are 
hence  perhaps  truly  Monophyodont. 

More  diversity  exists  in  the  premolar  and  molar  teeth  ; 
in  Rodents  of  mixed  diet,  such  as  the  common  rat,  the  back 
teeth  are  coated  over  the  crown  with  enamel,  which  nowhere 
forms  deep  folds,  and  have  distinct  roots,  i.e.,  are  not  of 
persistent  growth  ;  the  molars  of  the  rat  have  some  sort  of 
resemblance  to  minute  human  molars.  In  aged  specimens 
the  enamel  is  consequently  worn  off  the  grinding  surface  of 
the  crown,  which  comes  to  be  an  area  of  dentine,  surrounded 
by  a  ring  of  enamel. 

But  in  those  whose  food  is  of  a  more  refractory  nature, 
the  molars,  like  the  incisors,  grow  from  persistent  pulps  (as 
.  is  exemplified  in  the  Capybara  here  figured),  and  their 
working  surfaces  are  kept  constantly  rough  by  the  enamel 
dipping  in  deeply  from  the  side  of  the  tooth,  as  may  also  be 
seen  in  the  common  water-rat.  The  inflection  of  enamel 

(b  Molar  of  Capybara,  showing  the  transverse  plates  of  dentine  and 
enamel  united  to  one  another  by  cementum. 


THE  TEETH  OF  RODENT  I  A. 


365 


may  be  so  deep  as  to  divide  the  areas  of  dentine  completely 
up,  the  result  being  a  tooth  like  that  of  the  Capybara,  which 
is  composed  of  a  series  of  plates  of  dentine,  or  ‘denticles,’ 
surrounded  by  layers  of  enamel,  and  all  fused  together  by 
the  cementum.  The  result  of  this  disposition  of  the  struc- 


Fm.  151  p). 


tures  is  that  the  working  surface  is  made  up  of  enamel, 
dentine,  and  cementum,  three  tissues  of  different  hardness, 
which  will  consequently  wear  down  at  different  rates,  and 
so  maintain  its  roughness.  Various  intermediate  forms  of 
the  molar  teeth  are  met  with ;  thus  there  are  some  in 
which  complexity  of  the  surface  is  maintained  bjr  folds  of 
enamel  dipping  in  for  a  little  distance,  but  which  never¬ 
theless  after  a  time  form  roots  and  cease  to  grow.  When 
the  molar  teeth  grow  from  persistent  pulps,  they  are  always 
curved,  like  the  incisors,  with  the  effect  of  relieving  the 

(l)  Condyle  and  glenoid  cavity  of  the  Capybara,  showing  their  longitu¬ 
dinal  direction. 


366 


A  MANUAL  OF  DENTAL  ANATOMY . 


pulps  from  direct  pressure  during  mastication ;  and  the  last 
remains  of  the  pulps  are  converted  into  secondary  or  osteo- 
dentine,  which  thus  forms  the  central  axis  of  the  incisors,  or 
molars,  as  the  case  may  be.  In  this  tissue  vascular  tracts 
sometimes  exist,  but  it  is  altogether  small  in  amount,  the 
formation  of  true  dentine  going  on  till  the  pulp  at  that 
particular  point  is  almost  obliterated. 

As  has  already  been  mentioned,  when  the  molar  series 


Fig.  152  (!). 


consists  of  more  than  three  teeth,  those  anterior  to  the 
three  true  molars  are  premolars,  which  have  displaced  milk 
teeth  ;  but  they  do  not  differ  materially  in  size  or  form  from 
the  true  molars. 

The  form  of  the  condyle  and  of  the  glenoid  cavity  in 
Rodents  are  characteristic  ;  they  are  much  elongated  in  an 
antero-posterior  direction,  so  that  the  range  of  backward 
and  forward  motion,  made  use  of  in  gnawing,  is  very  con¬ 
siderable.  The  Leporidce  are  exceptional  in  having  more 
lateral  play  than  most  Rodents.  And  the  power  of  the 
teeth  is  marvellous ;  rats  will  sometimes  gnaw  holes  in 


(*)  Cranium  of  Capybara. 


THE  TEETH  OF  RODENTIA. 


367 


water-pipes,  or  in  gas-pipes,  in  which  they  have  heard  water 
bubbling. 

The  general  character  of  a  Rodent’s  dentition  may  be 
illustrated  by  a  description  of  that  of  the  Capybara. 

The  incisor  teeth  are  squarish.  They  are  wider  than  they 
are  deep,  and  are  slightly  grooved  on  their  anterior  surface. 

There  are  four  grinding  teeth  on  each  side,  of  which  the 
first  three  are  small,  and  with  few  cross  plates  of  dentine 
and  enamel,  but  the  fourth  is  a  very  complex  tooth,  with 
twelve  or  more  such  plates,  which  are  fused  into  a  solid 
mass  by  cementum. 

This  tooth  being  one  of  persistent  growth,  there  is  no 
common  pulp  cavity,  but  each  plate  has  its  own. 

It  has  already  been  mentioned  (page  170)  that  the  den¬ 
tinal  tubes  at  that  part  of  the  Rodent’s  incisor  which  has 
come  into  use  are  much  smaller  than  those  near  to  its 
growing  base,  thereby  proving  that  they  have  undergone  a 
diminution  in  calibre  at  a  time  subsequent  to  their  original 
formation.  Near  to  the  surface  actually  in  wear  they 
become  cut  off  from  the  pulp  cavity  by  the  conversion  of 
what  remains  of  the  pulp  into  a  laminated  granular  mass, 
so  that  the  dentine  exposed  on  the  surface  of  a  Rodent’s 
tooth  must  be  devoid  of  sensitiveness,  and  the  contents  of 
the  dentinal  tubes  must  have  presumably  undergone  some 
change.  But  what  the  nature  of  the  change  in  the  contents 
of  dentinal  tubes  which  have  ceased  to  be  in  continuity  with 
a  vascular  living  pulp  may  be,  there  are,  so  far  as  I  know, 
no  observations  to  indicate. 

As  was  shown  by  my  father  (Phil.  Trans.  1850),  the 
enamel  of  Rodents  is  peculiar,  and  some  little  diversity  in 
the  arrangement  of  the  prisms  exists  in  different  families  of 
the  order,  their  character  being  in  many  cases  so  marked, 
that  it  is  often  possible  to  correctly  refer  a  tooth  to  a  par¬ 
ticular  family  of  Rodents  after  simple  inspection  of  its 
enamel. 


368 


A  MANUAL  OF  DENTAL  ANATOMY. 


In  general  terms  it  may  be  said  that  the  enamel  is  divided 
into  two  portions,  an  outer  and  an  inner  portion  (this  is 
true  of  all  save  the  hares  and  rabbits),  and  that  the  enamel 
prisms  pursue  different  courses  in  these  two  portions. 

Thus  in  the  enamel  of  the  beaver,  in  the  inner  half,  nearest 
to  the  dentine,  the  prisms  of  contiguous  layers  cross  each 
other  at  right  angles,  whereas  in  the  outer  portion  they  are 
all  parallel  with  one  another. 

In  the  genera  Sciurus,  Pteromys,  Tamias,  and  Spermo- 
philus  the  enamel  fibres,  as  seen  in  longitudinal  section, 


Fig,  153  P). 


start  from  the  dentine  at  right  angles  to  its  surface ;  in 
Castor  they  incline  upwards  at  an  angle  of  60°,  but  preserve 
the  distinction  between  the  outer  and  inner  layers  very 
distinctly. 

In  the  Muridte  the  decussation  of  the  layers  in  the  inner 
part,  and  their  parallelism  in  the  outer  part  of  the  enamel 
are  also  found,  but  in  addition  to  this  the  borders  of  the 
individual  prisms  are  slightly  serrated,  the  serrations  of 
contiguous  fibres  interlocking. 

In  the  porcupine  sub-order  the  fibres  of  the  inner  portion 

(l)  Transverse  section  of  an  incisor  of  a  Beaver  (Castor  fiber).  The 
enamel  prisms  of  superimposed  layers  cross  each  other  at  right  angles  in 
the  inner  portion  of  the  enamel,  but  all  become  parallel  in  the  outer. 


THE  TEETH  OF  HYEACOIDEA. 


369 


of  the  enamel  pursue  a  serpentine  course,  nevertheless 
showing  indications  of  a  division  into  layers ;  they  become 
parallel  in  the  outer  portions  as  in  other  Rodents,.  Small 
insterspaces  are  found  amongst  the  enamel  fibres  of  the 
porcupines. 

In  the  hares  (Leporidse)  the  lamelliform  arrangement,  and 
the  division  into  outer  and  inner  layers,  alike  disappear. 

The  peculiarities  in  the  disposition  of  the  enamel  fibres, 
which  are  so  marked  in  the  incisors,  do  not  generally  exist 
in  the  molars  of  the  same  species. 

Many  minor  differences  in  the  arrangement  of  the  enamel 
prisms  exist,  for  a  description  of  which  I  must  refer  the 
reader  to  the  original  paper,  but  in  general  terms  it  may  be 
said  that  the  “  enamel  lamellae  have  a  different  and  distinc¬ 
tive  character  in  each  of  the  larger  groups,  and  that  the 
variety  of  structure  is  constant  throughout  the  members  of 
the  same  group  ;  we  may  take,  for  example,  the  Sciuridae, 
the  Muridae,  and  the  Hystricidae,  in  each  of  w7hich  the 
structure  of  the  enamel  is  different ;  and  in  each  is  highly 
distinctive.”  And  further,  that  the  varieties  in  the  struc¬ 
ture  of  the  dental  tissue,  so  far  as  they  are  known,  with  a 
few  isolated  exceptions,  justify  and  accord  with  the  classifi¬ 
cation  of  the  members  of  the  order  usually  given. 


THE  TEETH  OF  HYRACOIDEA. 

The  Biblical  coney  (Hyrax),  an  animal  as  large  as  a 
rabbit,  must  not  be  passed  over  without  mention,  as  its 
dentition  has  been  indirectly  the  source  of  much  contro¬ 
versy.  So  far  as  the  pattern  of  its  molar  teeth  goes,  it 
corresponds  closely  with  Rhinoceros,  and  was  hence  classed 
in  close  proximity  to  that  genus  by  Cuvier.  But  a  more 
extended  survey  of  its  characters  has  led  to  its  being  placed 


B  B 


370 


A  MANUAL  OF  DENTAL  ANATOMY . 


in  a  separate  sub-order ;  it  is  a  good  example  of  the  danger 
which  attends  relying  upon  any  single  character,  such  as 
the  pattern  of  the  teeth,  as  being  alone  a  sufficient  basis  for 
classification. 

All  observers,  however,  are  not  agreed  as  to  its  position 

Fig.  154  (*). 


it  certainly  presents  affinities  with  Perissodactyla,  but  most 
modern  zoologists  are  pretty  well  agreed  in  placing  it  in 
a  sub-order  by  itself.  Prof.  Cope,  however,  regards  it 
as  closely  akin  to  some  early  highly  generalised  Ungu¬ 
lates,  which  he  groups  together  by  the  name  of  Taxeopoda ; 
they  all  possessed  five  toes  on  each  foot,  and  many  of  the 
characters  of  their  teeth  bring  them  within  measurable 
distance  of  ancient  Insectivora. 


0)  Skull  of  the  Hyrax. 


THE  TEETH  OF  PROBOSCIDEA. 


371 


.  .  2  0  4  3 

The  dental  formula  is  i  c  q-  prm  m  * 

Seen  from  the  side,  the  dentition  bears  some  resemblance 
to  that  of  a  Rodent,  because  of  the  large  size  of  its  central 
incisors,  which  grow  from  persistent  pulps,  are  chisel-edged, 
prismatic  in  section,  and  are  furnished  with  a  very  thick 
coat  of  enamel  on  their  antero-external  and  antero-internal 
faces :  the  second  pair  of  incisors,  which  are  small,  are  soon 
lost.  But  Hyrax  has  the  full  typical  number  of  premolars 
and  molars,  and  the  patterns  of  these  teeth  are  closely  similar 
to  those  of  the  Rhinoceros. 

In  the  lower  jaw  the  middle  incisors  are  small,  and  the 
outer  ones  largely  developed,  and  all  persist  :  their  crowns 
are  in  a  manner  trilobed,  and  they  pass  in  ordinary  closure 
of  the  mouth  behind  the  upper  incisors,  where  they  are  met 
by  a  dense  pad  of  gum,  but  they  are  not  of  persistent 
growth. 


THE  TEETH  OF  PROBOSCIDEA. 


At  the  present  day  the  Elephant  stands  alone,  removed 
by  many  striking  peculiarities  from  the  Ungulata,  to  which 
it  is  more  nearly  allied  than  to  other  orders ;  but  in  former 
days  the  order  Proboscidea  was  represented  by  a  good  many 
genera,  was  widely  distributed  over  the  globe,  and  tran¬ 
sitional  forms  linking  the  elephant  with  somewhat  less 
aberrant  mammalia  were  not  wanting.  In  this  group  the 
incisors  grow  from  persistent  pulps,  and  form  conspicuous 


tusks ;  the  elephant  has  i 


the  Mastodon  has  i 


1 

1  ’ 


the 


Dinotherium  i — . 

1 


Two  striking  features  characterise  the  dentition  of  the 
elephant ;  the  enormous  length  of  the  incisor  tusks,  and 

e  b  2 


372 


A  MANUAL  OF  DENTAL  ANATOMY. 


the  peculiar  displacement  from  behind  forwards  of  the  molar 
teeth,  by  which  it  results  that  not  more  than  one  whole 
molar,  or  portions  of  two,  are  in  place  at  any  one  time. 

The  upper  tusks  are  preceded  by  small  deciduous  teeth  ; 
this  is  well  established,  though  it  has  been  recently  denied  by 
Sanderson  (Wild  Beasts  of  India).  When  first  cut  they 
are  tipped  with  enamel,  but  the  enamel  cap  is  soon  worn  off, 
and  the  remainder  of  the  tusk  consists  of  that  modification 
of  dentine  known  as  “  ivory,”  and  of  a  thin  external  layer  of 
cement.  In  some  extinct  species  the  enamel  formed  longi¬ 
tudinal  bands  upon  the  tusks. 

In  the  Indian  elephant  the  tusks  are  not  so  large  as  in  the 
African  species  :  and  the  tusks  of  the  female  are  very  much 
shorter  than  those  of  the  male.  In  the  African  elephant,  no 
such  difference  in  size  has  been  established ;  and  amongst 
Indian  elephants  males  are  sometimes  met  with  which  have 
tusks  no  larger  than  the  females  of  corresponding  size  ;  they 
go  by  the  name  of  “  Mucknas.”  This  peculiarity  is  not 
always  transmitted,  and  it  is  known  that  in  Ceylon  tuskless 
sires  sometimes  beget  “tuskers.”  Amongst  the  Ceylon 
elephants  the  possession  of  large  tusks  by  the  male  is  an  ex¬ 
ceptional  thing,  Sanderson  stating  that  only  one  in  three 
hundred  has  them,  while  amongst  51  Indian  elephants  only 
five  were  tuskless.  The  tusks  are  formidable  weapons,  and 
great  dread  of  a  “  tusker,”  is  shown  by  elephants  less  well 
armed. 

A  male  makes  use  of  his  tusks  for  all  sorts  of  purposes ; 
thus  when  a  tamed  one  is  given  a  rope  to  pull,  he  will,  by 
way  of  getting  a  good  purchase  upon  it,  pass  it  over  one 
tusk  and  grasp  it  between  his  molar  teeth. 

A  pair  of  African  tusks  exhibited  at  the  Great  Exhibition 
of  1851  weighed  325  lbs.,  and  measured  8  feet  six  inches 
in  length,  and  22  inches  in  circumference,  but  the  average 
tusks  imported  from  Africa  do  not  exceed  from  20  lbs.  to 
50  lbs.  weight.  Indian  elephants  seldom  have  tusks  attain- 


THE  TEETH  OF  PROBOSCIDEA 


373 


ing  very  large  dimensions  ;  one  was,  however,  shot  by  Sir 
Victor  Brooke  with  a  tusk  8  feet  long,  weighing  90  lbs. 

The  largest  tusks  were  possessed  by  the  Mammoth,  the 
remains  of  which  are  so  abundant  in  Siberia ;  these,  w'hich 
are  strongly  curved,  and  formed  a  considerable  segment 
of  a  circle  with  an  outward  inclination,  so  as  to  well  clear  the 
sides  of  the  head,  attained  the  length  of  13  feet,  and  a 
weight  of  200  lbs.  each. 

Ivory  is  one  of  the  most  perfectly  elastic  substances 
known,  and  it  is  on  this  account  that  it  is  used  for  billiard 
balls  ;  it  owes  its  elasticity  to  the  very  small  size  of  the 
dentinal  tubes  and  the  frequent  bends  (secondary  curva¬ 
tures)  which  they  make ;  to  the  arrangement  of  the  tubes 
the  peculiar  engine-turning  pattern  of  ivory  is  due.  It 
differs  from  other  dentine  in  its  containing  from  40  to  43 
per  cent,  of  organic  matter  (human  dentine  contains  only 
about  25),  and  in  the  abundant  concentric  rows  of  inter- 
globular  spaces.  Along  these  ivory  when  it  decomposes 
breaks  up,  so  that  a  disintegrated  segment  of  a  tusk  con¬ 
sists  of  detached  concentric  rings  ;  in  this  condition  many 
mammoth  teeth  are  found,  although  sometimes  where  they 
have  remained  frozen  and  protected  from  the  air  until  the 
time  of  their  discovery  they  are  hardly  affected  by  the  lapse 
of  the  thousands  of  years  which  have  gone  by  since  their 
possessors  perished. 

The  best  ivory  is  that  which  comes  from  equatorial 
Africa ;  Indian  ivory  is  not  so  highly  esteemed,  and  mam¬ 
moth  ivory  is  so  uncertain  in  its  degree  of  preservation 
that  it  does  not  find  a  ready  sale,  even  though  some  samples 
almost  attain  the  quality  of  recent  ivory. 

The  last  remains  of  the  pulp  are  converted  into  dentine 
in  which  a  few  vascular  canals  persist ;  this  of  course  occu¬ 
pies  the  centre  of  the  tusk,  and  is  small  in  amount. 

The  trade  in  ivory  is  quite  an  important  one,  the 
Board  of  Trade  returns  for  1879,  giving  9414  cwts.,  of 


374 


A  MANUAL  OF  DENTAL  ANATOMY. 


the  value  of  £406,927,  as  the  quantity  brought  to  this 
country. 

But  the  best  of  mammoth  ivory,  which  has  been 
preserved  by  the  low  temperature  from  any  change,  so 
that  it  is  hardly  distinguishable  from  recent  ivory,  has  long- 
been  an  article  of  commerce,  perhaps  even  from  the  time  of 
Pliny. 

Nordenskiold  (Voyage  of  the  Vega)  mentions  that  the 
dredge  often  brought  up  portions  of  tusks,  and  the  natives 
offered  at  times  very  fine  tusks  for  sale. 

It  is  estimated  that  100  pairs  annually  come  thus  into  the 
market,  and  this  is  probably  less  than  the  real  number. 
He  travelled  up  the  Yenisei  in  1875  on  board  a  steamer 
which  carried  over  100  tusks,  of  which,  however,  a  large 
number  were  so  blackened  and  damaged,  that  it  was 
difficult  to  suppose  them  marketable. 

The  nearer  you  get  to  the  Polar  coasts  the  more 
abundant  are  the  mammoth  remains,  especially  where 
there  have  been  great  landslips,  though  the  tusks  found 
at  the  lowest  latitudes  are  said  to  be  smaller. 

In  the  new  Siberian  Islands,  in  the  space  of  a  verst,  he  saw 
ten  tusks  sticking  out  of  the  ground,  and  from  a  single  sand¬ 
bank  ivory  collectors  have  for  eighty  years  reaped  a  harvest. 

In  England  dealers  in  ivory  seem  all  to  deny  ever  using 
mammoth  ivory,  though  the  finest  specimens  require  the 
eye  of  an  expert  to  distinguish  them  from  recent  ivory 
when  cut  up,  and  the  denial  must  be  taken  cum  grano. 

The  surfaces  of  the  tusks  of  the  female  are  often  deeply 
excavated  about  the  level  of  the  edge  of  the  gum,  and  are 
sometimes  so  weakened  from  this  cause  that  they  break  off. 
My  friend  Prof.  Moseley  tells  me  that  he  was  informed  by  the 
late  Major  Bossall,  who  as  a  sportsman  had  great  knowledge 
of  Indian  elephants,  that  the  tusks  of  all  the  females  he  has 
ever  seen  are  so  affected,  and  that  the  larvae  or  pupae  of  a 
dipterous  insect  are  often  found  bedded  in  the  gum,  and 


THE  TEETH  OF  PROBOSCIDEA. 


375 


attached  to  the  surface  of  the  tusk.  There  is  a  specimen  of 
a  female  elephant’s  tusk  with  the  pupae  attached  in  the 
Museum  of  the  Royal  College  of  Surgeons.  It  would  be  a 
matter  of  interest  to  ascertain  whether  the  larva  really  eats 
away  the  tusk,  or  whether  the  wasting  of  the  tusk  be  due 
to  absorption  set  up  by  the  irritated  gum. 

The  tusks  of  an  elephant  are  implanted  in  long  and 
stout  sockets,  and  grow  from  persistent  pulps  throughout 
the  lifetime  of  the  animal. 

In  the  Indian  elephant  about  one  half  of  the  length  of  the 
tusk  is  implanted,  and  in  young  animals  the  pulp  cavity 
extends  beyond  the  implanted  portion,  but  in  older  animals 
it  does  not  extend  nearly  so  far.  A  knowledge  of  its  extent 
is  necessary,  seeing  that  the  tusks  of  captive  elephants  have 
to  be  shortened  from  time  to  time;  this  operation  is  by 
some  done  frequently,  by  others  only  at  long  intervals,  such 
as  ten  years,  in  which  case  a  large  and  valuable  segment  of 
ivory  is  cut  off,  and  the  end  of  the  tusk  bound  with  metal 
to  prevent  it  from  splitting. 

Tusks  sometimes  exemplify  on  a  large  scale  the  results  of 
injury  to  the  growing  pulp,  as  it  is  of  no  unfrequent  oc¬ 
currence  that  elephants  wThich  have  been  shot  at  and 
wounded  escape. 

The  thin  walls  of  the  tusk  near  to  its  open  end  do  not 
offer  very  much  resistance  to  the  entrance  of  a  bullet ;  the 
result  of  such  an  injury  is  not,  as  might  have  been  expected, 
the  death  of  the  pjrilp,  but  in  some  cases  abscess  cavities 
become  formed  in  the  neighbourhood  of  the  injury,  wdiile 
in  others  less  disturbance  is  set  up,  the  bullet  becomes 
enclosed  in  a  thin  shell  of  secondary  dentine,  or  sometimes 
lies  loose  in  an  irregular  cavity,  and  round  this  the  normal 
“  ivory  ”  is  deposited  ;  upon  the  outside  of  the  tusk  no  indi¬ 
cation  of  anything  unusual  is  to  be  seen,  so  that  the  bullets 
thus  enclosed  are  found  by  ivory  turners  only  wdien  sawing 
up  the  tusk  for  use. 


376 


A  MANUAL  OF  DENTAL  ANATOMY. 


As  the  tusk  grows,  that  which  was  once  in  the  pulp 
cavity,  and  within  the  alveolus,  comes  to  be  at  a  distance 
from  the  head,  and  in  the  midst  of  solid  ivory. 

As  an  example  of  the  extent  of  injury  from  which  a 
tooth  pulp  is  capable  of  recovery,  may  be  cited  a  specimen 
now  deposited  in  the  Museum  of  the  Odontological  Society, 
by  Mr.  Bennett,  to  whom  I  am  indebted  for  permission  to 
figure  it. 

It  is  to  be  presumed  that  a  trap  was  set  with  a  heavily 
loaded  spear,  or  that  it  was  dropped  by  a  native  from  a 
tree,  with  the  intention  of  its  entering  the  brain  of  the 


Fig.  155  (J). 


elephant  as  it  was  going  to  water,  both  of  these  methods  ,  of 
killing  elephants  being  practised  in  Africa.  But' in  this  case 
the  spear  penetrated  the  open  base  of  the  growing  tusk, 
which  looks  almost  vertically  upwards  (see  fig.  155),  and 
then  the  iron  point  appears  to  have  broken  off.  This  did 
not  destroy  the  pulp,  but  the  tooth  continued  to  grow,  and 
the  iron  point,  measuring  no  less  than  by  H  inches, 
became  so  completely  enclosed  that  there  was  nothing  upon 
the  exterior  of  the  tusk  to  indicate  its  presence. 

I  am  told  by  Mr.  Erxleben  that  he  is  acquainted  with 
another  instance  in  which  a  spear  head  has  become  com¬ 
pletely  enveloped  in  ivory. 

(b  Iron  spear-Iiead,  irremovably  fixed  in  the  interior  of  a  tusk,  believed 
to  be  from  an  African  Elephant.  From  a  specimen  in  the  possession  of 
Mr.  Bennett. 


377 


I 


THE  TEETH  OF  PROBOSCIDEA. 


There  are  also  other  specimens  extant,  of  which  an 
excellent  example  is  a  javelin  head  quite  solidly  embedded 
in  the  ivory,  which  is  in  the  Museum  of  the  Royal  College 
of  Surgeons. 

Six  molar  teeth  are  developed  on  each  side  of  the  jaw  by 
the  elephant,  and,  arguing  from  analogy,  they  are  some¬ 


times  classified  thus — milk  molars 


3 

3 


true 


molars 


3 

3  9 


occasionally  a  rudimentary  tooth  in  front  brings  up  the 
number  to  seven  on  each  side.  But  the  peculiarity  of  their 
mode  of  succession  renders  such  a  classification  merely 
arbitrary,  so  far  as  the  elephant  itself  is  concerned,  and  it 
depends  upon  analogy  with  the  teeth  of  the  mastodon. 
Though  the  elephant  has,  during  the  course  of  its  life? 
twenty-four  molars,  they  are  not  all  in  place,  nor  indeed 
are  they  all  actually  in  existence  at  the  same  time.  Only 
one  whole  tooth  on  each  side,  or  portions  of  two  (when  the 
front  one  of  the  two  is  nearly  worn  out),  are  in  use  at  the 
same  time.  After  a  tooth  has  been  in  use  for  some  time, 
and  is  worn  down,  a  new  tooth  comes  up  to  take  its  place 
from  behind  it,  and  absorption  in  the  old  tooth  being  set  up, 
it  is  shed  off,  and  the  new  tooth  pushes  forward  into  its 
place  (see  fig.  156).  Each  successive  tooth  is  of  greater 
size  than  its  predecessors  ;  thus  in  the  Indian  elephant  the 
first  tooth  having,  on  an  average,  four  transverse  plates ; 
the  second  eight,  the  third  twelve,  the  fourth  twelve,  the 
fifth  sixteen,  the  sixth  from  twenty-four  to  twenty-seven. 
In  the  African  elephant,  in  which  the  individual  plates  are 
much  broader,  they  are  fewer  in  number. 

A  reference  to  the  accompanying  figure  will  indicate  how 
the  succession  takes  place.  The  tooth  in  reserve  occupies  a 
position  at  an  angle  to  that  in  use ;  as  it  moves  forwards 
and  (in  the  upper  jaw)  downwards  its  track  forms  almost 
the  segment  of  a  circle.  Thus  its  anterior  corner  is  the 
first  to  come  into  use,  at  a  time  when  the  position  of  the 


373 


A  MANUAL  OF  DENTAL  ANATOMY. 


whole  tooth  is  still  exceedingly  oblique,  and  the  greater  part 
of  it  is  still  within  the  socket. 

The  teeth  as  first  formed  consist  of  detached  plates  of 


Fig.  156  (*). 


dentine  coated  with  enamel,  the  tops  of  which  are  mammil- 
lated ;  these  only  coalesce  after  a  considerable  portion  of 
their  depth  has  been  formed,  and  that  portion  of  the  tooth 
has  been  reached  in  which  there  is  a  common  pulp  cavity ; 

P)  Side  view  of  skull  of  young  Indian  Elephant.  The  teeth  in  use  are 
the  second  and  third  of  the  molars  which  displace  one  another  from 
behind  forwards  ;  the  anterior  of  these,  corresponding  to  a  milk  molar  in 
other  animals,  is  nearly  worn  out ;  the  residual  fragment  is  separately 
represented  on  the  left.  The  tusk,  of  which  only  a  short  piece  can  be 
shown,  is  indicated  within  the  socket  by  dotted  lines,  by  which  also  the 
form  of  the  pulp  cavity  is  mapped  out. 


THE  TEETH  OF  PROBOSCIDEA. 


379 


here  dentine  is  continuous  from  end  to  end  of  the 
tooth. 

Just  as  the  cusps  of  a  human  molar  are  separate  when 
first  calcified,  so  these  exaggerated  cusps  or  plates  of  an 
elephant’s  tooth  are  separate  from  one  another  till  a  great 
part  of  their  length  is  completed,  and  they  only  coalesce 
when  they  reach  the  level  of  the  common  pulp  chamber ;  in 
point  of  fact  the  elephant’s  tooth  is  mainly  made  up  of  its 
cusps,  the  remaining  portion  being  insignificant. 

Several  of  these  detached  plates,  such  as  the  one  here 
figured,  are  to  be  found  at  the  back  of  the  largest  teeth 
even  at  a  time  when  the  front  corner  has  been  erupted  and 
has  come  into  wear. 

That  the  tooth  is  thus  being  built  up  only  as  it  is  required 
is  of  obvious  advantage  to  the  animal  in  diminishing  the 
weight  to  be  carried,  and  is  also  an  economy  of  space. 

The  teeth  when  they  begin  to  be  erupted  do  not  at  once 
come  into  use  over  their  whole  surface,  but  they  come  for¬ 
ward  in  an  oblique  position,  so  that  the  front  of  the  tooth 
has  been  in  use  for  some  time,  and  its  plates  have  been  con¬ 
siderably  worn  down,  before  the  back  of  the  tooth  has 
become  exposed  at  all.  Nay,  more,  in  the  case  of  the  larger 
molars  the  front  of  the  tooth  is  actually  in  use  at  a  time 
when  its  back  is  not  yet  completed. 

In  the  elephant  there  is  no  vertical  succession  of  teeth 
whatever;  the  manner  of  succession  usual  amongst  mammals 
has  in  them  given  place  to  a  succession  from  behind,  the 
older  teeth  being  pushed  out  forwards.  Had  the  elephant 
always  been  as  isolated  a  form  as  it  now  appears  to  be,  it 
would  have  been  very  uncertain  how  its  six  molars  should 
be  classified.  But  it  happens  that  proboscideans  formerly 
existed  in  which  this  peculiar  succession  from  behind  was  to 
be  found,  at  the  same  time  that  the  ordinary  vertical  suc¬ 
cession  was  not  quite  lost,  and  amongst  these  creatures  (the 
mastodons)  we  are  able  to  say  with  certainty  which  of  the 


380 


A  MANUAL  OF  DENTAL  ANATOMY. 


teeth  are  milk  molars,  which  are  premolars,  and  which  are 
true  molars.  And  as  the  mastodons  pass  by  insensible  gra¬ 
dations  into  the  elephants,  so  that  the  line  of  demarcation 
between  the  two  genera  is  an  arbitrary  one,  we  can  tell 


Fig.  157  l1). 


which  of  the  mastodon’s  teeth  correspond  to  each  one  of  the 
six  molars  of  the  elephant. 

Mastodon. — In  the  later  tertiary  periods  this  genus,  ap¬ 
proximating  in  its  dental  and  other  characters  to  the  true 
elephant,  was  widely  distributed  over  the  world.  The  dental 
formula  is  not  quite  the  same  for  all  the  genus,  for  in  some 
no  premolars  existed. 

.10  2  ,  3  3 

i  —  c  —  pm  —  milk  molars  -  m  . 

1  0  1  2  3  3 

The  upper  incisors  formed  nearly  straight  tusks,  seven  or 
eight  feet  in  length ;  the  lower  incisors  also  grew  out  hori¬ 
zontally  from  the  front  of  the  jaw,  but  in  some  species  the 
lower  tusks  are  rudimentary,  are  lost  early,  or  are  altogether 

(')  Isolated  plate  (=  exaggerated  cusp)  of  an  Elephant’s  tooth,  prior  to 
its  coalescence  with  neighbouring  plates  ;  at  the  top  are  seen  its  terminal 
mammillated  processes,  one  of  which  has  been  cut  off  to  show  the  central 
area  of  dentine,  surrounded  by  enamel ;  at  the  base  would  be  the  open 
pulp  cavity,  not  shown  in  the  figure. 


THE  TEETH  OF  PROBOSCIDEA. 


381 


absent,  thus  more  nearly  approaching  to  the  condition  met 
with  in  the  elephant. 

The  several  molar  teeth  of  the  Mastodon  increased  in 
size  from  before  backwards.  The  crowns  were  built  up  of 
deep  and  strongly  pronounced  transverse  ridges,  of  which 
the  last  molar  had  the  largest  number.  The  apices  of  the 
ridges,  before  being  at  all  worn,  were  divided  up  into  several 
blunt  nipple  -  like  (mastoid)  processes,  upon  which  the 
enamel  was  thick  and  dense,  but  the  cement  was  thin,  so 
that  the  interspaces  of  the  processes  were  not  filled  up  level 
by  the  latter  tissue,  as  in  the  elephant. 

Very  definite  roots  were  formed  to  the  molars,  the  wear¬ 
ing  down  of  the  teeth  being  met  by  the  worn  teeth  being 
shed  off  altogether  from  the  front  of  the  series,  whilst  new 
teeth  were  added  to  the  back.  Thus,  just  as  in  the  elephant, 
the  whole  number  of  teeth  were  not  in  place  at  one  time. 
Not  more  than  three  were  in  use  at  one  time,  and  by  the 
time  the  last  and  largest  molar  was  cut,  there  was  but  one 
tooth  remaining  in  front  of  it,  and  even  this  was  soon  lost,  the 
dentition  thus  being'  reduced  to  a  single  molar  on  each  side. 

As  the  succession  of  the  molars  in  the  Mastodon  affords 
a  clue  to  the  nature  of  the  grinders  of  the  elephant,  it  is 
necessary  to  add  a  few  words  about  it.  Some  Mastodons 
had  three  milk  molars,  of  which  the  last  two  were  vertically 
displaced  by  premolars,  just  as  in  most  other  mammals, 
but  the  first  milk  molar  was  not  so  replaced  (Mastodon 
angustidens).  There  appear  to  have  been  Mastodons  in  which 
no  vertical  succession  at  all  took  place,  i.e.}  in  which  there 
were  no  premolars,  and  others  in  which  there  was  but  one. 

No  doubt  can  be  entertained  as  to  the  homologies  of  the 
teeth,  even  in  those  Mastodons  which  are  not  known  to 
have  any  vertical  succession,  because  analogy  with  those 
other  species  in  which  the  second  and  third  molars,  counted 
from  the  front,  were  vertically  displaced  by  nearly  function¬ 
less  premolars,  tells  us  that  the  three  front  molars  are  milk 

I  dr.  b.  Walter 


382 


A  MANUAL  OF  DENTAL  ANATOMY. 


molars.  Now  elephants  develop  six  molar  teeth  on  each  side; 
the  elephant  is  in  the  same  case,  quoad  its  molars,  as  the 
Mastodon  Ohioticus,  which  had  no  vertical  succession,  so  that 
we  thus  know  the  elephant’s  grinders  to  be 

,33 

dm  -  m  -  . 

3  3 

Dr.  Falconer  mentions  an  elephant  from  the  Sewalik  Hills 
(E.  planifrons)  in  which  two  rudimentary  premolars,  of  no 
functional  importance,  actually  existed,  and  so  the  determi¬ 
nation  of  the  elephant’s  working  teeth  as 

.3  3 

dm  -  m  - 

3  3 

rests  not  only  upon  analogy,  but  upon  actual  observation. 

The  Dinotherium,  a  large  animal,  not  unlike  the  Sirenia 
in  the  character  of  its  cranium,  which  was  probably  of 
aquatic  habits,  was  remarkable  for  possessing  large  tusks,  by 
analogy  known  to  be  incisors,  in  its  lower  jaw,  none  being 
present  in  the  upper  jaw.  The  tusks  projected  downwards 
at  right  angles  with  the  body  of  the  jaw  and  were  curved 
backwards.  The  portion  of  jaw  about  the  symphisis  was 
deflected  downwards,  so  as  to  afford  an  adequate  implanta¬ 
tion  for  these  anomalous  tusks. 

The  dentine  of  these  tusks  does  not,  however,  present  the 
characteristic  ivory  pattern. 

The  Dinotherium  was  as  large  as  an  elephant,  and  the 
downward  pointing  tusks  were  about  2  feet  in  length  ;  as, 
however,  tusks  of  only  half  this  length  were  found  in  some 
jaws  of  identical  dimensions  and  in  other  respects  similar,  it 
is  believed  that  the  male  Dinotherium  had  larger  tusks  than 
the  female.  The  molar  teeth,  much  like  those  of  a  tapir, 
need  not  detain  us. 

.0  0  2  3 


1  0 


pm  ~  m 


THE  TEETH  OF  PROBOSCIDEA. 


383 


The  succession  was 


had 


vertical,  as  in  other  mammals,  and  it 


Fig.  158  ('). 


But  the  Dinotherium,  Mastodon,  and  Elephant,  present 
us  with  a  very  instructive  series  of  modifications  in  which 
we  see  how  the  excessively  complex  grinder  of  the  Indian 
elephant  was  attained  to  by  degrees. 

The  molar  of  the  Dinotherium  resembles  that  of  a  tapir 
somewdiat ;  it  has  not  any  very  great  exaggeration  of  its 
cusps,  and  does  not  deviate  very  widely  from  the  form  of 
many  other  mammalian  teeth. 

(!)  Skull  of  Dinotherium,  after  Owen. 


384 


A  MANUAL  OF  DENTAL  ANATOMY. 


The  tooth  of  Mastodon  has  its  cusps  or  ridges  more 
numerous  and  more  pronounced,  as  is  seen  in  the  accom¬ 
panying  figure. 

Fio.  159  (1). 


Fig.  160  (2). 


(*)  Molar  tooth  of  Mastodon. 

(2)  Molar  of  African  Elephant.  E.  Enamel.  D.  Dentine.  C.  Cementuin. 

(3)  Molar  tooth  of  African  Elephant,  showing  the  form  of  its  roots,  &c. 
a.  Dentine,  c.  Cementum.  e.  Enamel. 


THE  TEETH  OF  PROBOSCIDEA. 


385 


Other  Mastodons  have  more  numerous  ridges  upon  the 
teeth,  and  the  African  elephant  has  as  many  as  ten  upon 
its  last  or  larger  molar,  although  in  it  the  ridges  are  in¬ 
dividually  wide  and  strongly  pronounced. 

In  the  Indian  elephant  the  ridges  or  plates  are  still  more 
numerous,  the  roots  very  inconspicuous  and  the  whole  formed 
into  a  solid  block  by  cementum. 

The  gradual  increase  in  complexity  in  the  “ridge  formula ” 


Fig.  162  ('). 


(or  number  of  ridges  in  each  tooth),  of  the  molars,  is  well 
seen  in  the  following  table,  from  Prof.  Flowers  Hunterian 
lecture  (“Nature,”  March  2,  1876);  it  is  a  corrected  table 
taken  from  Dr.  Falconer’s  “Palaeontological  Memoirs.” 


Milk  Molars. 

True  Molars. 

Total. 

- 

I. 

II. 

ill. 

I. 

II. 

III. 

Dinotheriura  giganteum  . 

1 

2 

3 

3 

2 

2 

13 

Mastodon  (Trilophodon)  americanus 

1 

2 

3 

3 

3 

4 

16 

„  (Tetralophodon)arvernensis 

2 

3 

4 

4 

4 

5 

22 

,,  (Pentalophodon)  sivalensis 

3 

4 

5 

5 

5 

6 

28 

Elephas  (Stegodon)  insignis  .  .  . 

2 

5 

7 

n 

i 

8 

10 

39 

„  (Loxodon)  africanus 

3 

6 

7 

7 

8 

10 

41 

„  „  meridionalis  .  . 

3 

6 

8 

8 

9 

12 

46 

.  ,,  (Euelephas)  antiquus  . 

3 

6 

10 

10 

12 

16 

57 

,,  „  primigenius  .  . 

4 

8 

12 

12 

16 

24 

76 

,,  „  indicus 

4 

8 

12 

12 

16 

24 

76 

(!)  Molar  tooth  of  an  Asiatic  Elephant,  showing  the  transverse  plates  of 
dentine  bordered  by  enamel. 


c  c 


38(5 


A  MANUAL  OF  DENTAL  ANATOMY. 


Some  variability  exists  in  the  number  of  ridges,  especially 
when  they  are  very  numerous,  but  the  above  may  be  taken 
as  averages  ;  and  some  species  intermediate  in  the  “  ridge 
formula”  have  been  since  discovered;  thus  M.  Pentelici  and 
M.  Andium  bridge  the  distinction  between  Trilophodon  and 
Tetralophodon,  and  Elephas  melitensis  comes  between 
Loxodon  and  Euelephas  (Flower). 

It  remains  to  describe,  somewhat  more  in  detail,  the 
structure  of  an  elephant’s  tooth,  and  this  has  been  deferred 
till  the  last,  because  it  can  be  the  more  easily  understood 
when  the  manner  of  its  origin  has  been  mastered.  In  the 
Mastodon  the  molar  consists  of  a  crown  with  strong  cusps 
standing  apart,  and  with  marked  roots ;  in  the  African 
elephant  that  part  which  consists  of  cusps  has  become  the 
greater  bulk  of  the  tooth,  the  roots  are  comparatively  in¬ 
significant,  and  the  interspaces  of  the  cusps  are  filled  up  with 
cementum.  The  molar  of  the  Indian  elephant  consists  of  a 
larger  number  of  yet  more  elongated  and  flattened  cusps,  so 
that  the  greater  part  of  the  tooth  is  made  up  of  these  flattened 
plates,  fused  together  with  cementum,  and  so  forming  a  strong 
and  solid  mass ;  the  roots  are  comparatively  inconspicuous. 

When  the  tooth  is  a  little  worn  each  plate  consists  of  an 
area  of  dentine  surrounded  by  enamel.  The  interspaces 
of  the  series  of  plates  are  wholly  filled  up  by  cementum ; 
the  summits  of  each  plate  were  originally  mammillated, 
and  divided  up  into  more  numerous  blunt  processes  than 
the  corresponding  parts  of  the  tooth  of  a  Mastodon;  when 
the  tooth  comes  into  use  the  rounded  tips  are  soon  worn 
oft1',  and  the  grinding  surface  of  the  tooth  then  consists  of 
narrow  transverse  bands  of  dentine,  surrounded  by  enamel, 
and  of  cementum  in  their  interspaces.  The  difference  in 
hardness  between  these  three  tissues  preserves  a  constant 
rough  surface,  owing  to  their  unequal  rate  of  wear.  In  their 
wild  condition  elephants  eat  trees  with  succulent  juicy  stems, 
and  oftentimes  grass  torn  up  by  the  roots,  from  which  they 


THE  TEETH  OF  UNGULATE. 


387 


roughly  shake  out  the  adherent  earth.  In  confinement,  the 
food  containing  less  that  is  gritty,  the  teeth  become  polished 
by  working  against  one  another,  but  the  rate  of  wear  is  insuf¬ 
ficient  to  keep  their  surfaces  rough  ;  for  the  softer  cementum 
does  not  get  worn  down  in  the  interspaces  of  the  plates  of 
dentine  and  enamel,  but  remains  on  a  level  with  them. 

The  celebrated  elephant  “Jumbo”  suffered  from  insufficient 
wear  of  his  teeth,  so  that  the  earlier  ones  being  insufficiently 
worn  were  not  got  rid  of  at  the  proper  time,  and  interfered 
with  the  normal  development  of  their  successors. 

Great  though  the  size  of  the  Proboscideans  be,  they  have 
some  points  of  affinity  with  the  Rodents  in  the  great 
development  of  the  incisors,  the  vacant  interval  between 
these  and  the  molar  teeth,  and,  as  was  pointed  out  by  the 
late  Professor  Rolleston,  the  enamel  of  the  elephant’s  molar 
having,  in  its  inner  portions,  a  pattern  produced  by  the 
decussation  of  the  prisms,  which  is  very  similar  to  that 
described  by  my  father  as  characteristic  of  all  the  Rodents 
save  the  Leporidm  (Hares),  and  Hystricidse  (Porcupines). 


THE  TEETH  OF  UNGULATA. 

This  is  a  group  of  animals  of  which  a  vast  number  of 
forms  are  extinct,  and  are  only  imperfectly  known  to  us. 

Recent  discoveries,  especially  those  of  Professor  Marsh  in 
the  Mau vaises  Terres  of  Wyoming,  have  brought  to  light  a 
very  large  number  of  strange  and  highly  interesting  forms, 
which  have  broken  down  the  old  classification  of  Ungulates 
into  the  Artiodactyle  and  Perissodactyle  Ungulates,  and  have 
brought  within  it,  by  means  of  links,  to  a  certain  extent, 
Hyracoidea  and  Proboscidea. 

Nowadays,  provisionally,  they  may  be  grouped  into 
Ungulata  Vera  and  Subungulata. 


c  c  2 


388 


A  MANUAL  OF  DENTAL  ANATOMY. 


The  Ungulata  Yera  comprise — 

(i.)  Artiodactyles,  or  )  Hippopotamus,  Pigs,  Anoplotherium, 
even-toed  Ungulata  j  Cows,  Sheep,  Deer,  and  other  Ruminants, 
(ii.)  Perissodactyles,  or  \ 

Ungulata  with  an  |  Horses,  Tapirs,  Rhinoceros,  Palseotherium. 
odd  number  of  toes  ; 

The  distinction  between  the  two  groups  is  strongly  marked,  if 
living  animals  alone  be  considered  ;  but,  as  Professor  Huxley  has 
pointed  out,  increasing  knowledge  of  fossil  forms  has  broken  down 
the  line  of  demarcation. 

Then  we  have  an  ill-defined  group  of — 

Ungulata  Polydactyla  or  )  Hyracoidea,  Proboscidea,  and  Ambly- 

Subungulata,  comprising  j  poda,  and  perhaps  others. 

The  Amblypoda  comprise  a  number  of  extinct  animals  of  huge 
size,  as  big  as  elephants.  Prof.  Cope  includes  in  it  Prof.  Marsh’s 
order  Dinocerata,  and  to  it  may  perhaps  be  referred  several  forms 
whose  affinities  are  very  puzzling,  such  as  Toxodon. 

But  fortunately  it  is  not  necessary  in  an  elementary  work  on 
Odontology  to  do  more  than  present  the  descriptions  of  the  several 
creatures  somewhere  near  their  right  places,  and  so  the  increasing 
difficulties  of  the  classification  of  the  Ungulata  need  not  be  discussed. 

Of  Eocene  Ungulata  it  may  be  said  that  almost  all  pos¬ 
sessed  the  full  mammalian  dentition,  i.e. 

.31  4  3  AA 

1 3  c  r  pm  4  m  3  = 44 

and  a  few  had  more. 

Moreover  as  we  look  at  the  patterns  of  the  molar  teeth, 
we  find  them  far  more  simple,  trituberculate  or  quadri- 
tuberculate  crowns  being  the  rule.  Many  of  them  have  five 
toes,  and  were  otherwise  less  specialised  than  modern  forms. 
Ungulates  mostly  have  a  well  developed  milk  dentition, 
which  in  the  case  of  modern  domesticated  animals  remain 
in  use  for  a  long  time. 

The  Teeth  of  Perissodactyle  Ungulates.  —  Perisso- 
dactyle  (odd-toed)  Ungulates  are  far  less  numerous  than  the 
even-toed  section,  and  amongst  recent  animals  only  comprise 
the  Horse,  the  Rhinoceros,  the  Tapir  and  their  allies.  Their 
premolars,  or  at  least  the  last  three  of  them,  are  equally 


THE  TEETH  OF  PERISSODA CTYLE  UNGULATA.  389 


complex  in  pattern  with  the  true  molars ;  and  canines,  tusk¬ 
like  but  not  very  large,  are  of  frequent  occurrence.  The 
lower  molars  of  almost  all  perissodactyles  have  a  character¬ 
istic  form,  their  grinding  surfaces  being  made  up  of  two 
crescentic  ridges. 

The  ungulate  animals  are  all  possessed  of  molar  teeth, 
which  are  kept  in  an  efficient  state  of  roughness  by  the 
enamel  dipping  deeply  into  the  crowns  ;  by  the  cusps,  in 
fact,  being  of  very  great  depth.  It  consequently  happens 
that  after  the  immediate  apex  is  worn  away,  the  flattened 
working  face  of  the  tooth  is  mapped  out  into  definite 
patterns,  which,  on  account  of  the  light  thus  thrown  upon 
fossil  remains,  often  consisting  of  little  else  than  the  teeth, 
have  been  studied  with  great  care.  The  result  has  been  to 
establish  a  general  community  of  type,  so  that,  dissimilar 
as  they  at  first  sight  appear,  it  is  possible  to  derive  all,  or 
almost  all,  the  configurations  of  their  crowns  from  one  or 
two  comparatively  simple  patterns.  But  odontologists  are 
not  yet  agreed,  or  rather  do  not  yet  know  enough  of  the 
vast  number  of  extinct  Ungulates  which  there  is  reason  to 
believe  once  existed  (of  which  many  have  lately  been 
discovered)  to  decide  with  certainty  what  the  parent  pattern 
was. 

The  patterns  of  the  molars  have  been  made  use  of  to  divide 
them  into  the  following  groups  : 

(i.)  Bilophiodont,  i.e.  two  ridged,  e.g.  the  Tapir. 

(ii.)  Molars  (lower)  bicrescentic,  e.g.  Rhinoceros. 

(iii.)  Lower  molars  bicrescentic,  with  the  addition  of  inner 
lobes  or  columns,  e.g.,  Horse. 

The  Tapir  is  interesting  as  appearing  in  Miocene  strata 
and  remaining  practically  unchanged  till  the  present  time,  it 
being  thus  the  oldest  existing  genus  of  mammals  (Flower). 

Tapir. — The  dental  formula  is 


390 


A  MANUAL  OF  DENTAL  ANATOMY 


In  a  brief  survey,  like  that  to  which  the  present  work  is 
necessarily  confined,  it  will  suffice  to  mention  that  there  is 
no  great  peculiarity  about  the  incisors  or  the  canines,  save 
that  the  third  upper  incisor  is  larger  than  the  canine,  and 
opposes  the  lower  canine  which  ranges  with  the  lower  incisors ; 

Fig.  163  (l). 


behind  the  canine  comes  an  interval,  after  which  come  the 
premolars  and  molars,  which  are  interesting,  as  being  of 
simpler  pattern  than  those  of  most  Ungulates,  and  it  will  be 
necessary  to  very  briefly  allude  to  the  various  patterns 
characteristic  of  ungulate  teeth,  with  a  view  of  showing  how 
they  may  have  been  derived  the  one  from  the  other. 

The  first  upper  premolar  is  triangular,  one  of  its  cusps 
being  suppressed,  but  the  rest  of  them  are  squarish  and 
resemble  true  molars. 

In  the  Tapir  four  cusps  are  traceable,  but  ridges  uniting 
the  two  anterior  and  the  two  posterior  cusps  are  strongly 
developed,  at  the  cost  of  the  antero-posterior  depression,  ie.,  of 
one  of  the  arms  of  the  cross  which  separate  the  four  cusps 
in  other  quadricuspid  molars.  There  is  therefore  only  a 
deep  transverse  fissure  (hence  it  is  called  a  bilophiodont 
tooth),  and  the  quadricuspid  form  is  disguised.  A  low  wrall 
on  the  outside  of  the  tooth  connects  the  two  ridges. 

In  Rhinoceros  the  two  external  cusps  are  united  by  a 
longitudinal  ridge,  possibly  the  cingulum,  and  the  transverse 

(])  Grinding  surface  of  tooth  of  Tapir. 


THE  TEETH  OF  PERISSODACTYLE  UNGULATA.  391 


ridges  become  oblique ;  consequently  the  valley  between 
the  ridges  c  and  d  is  also  oblique  in  direction,  and  a 
second  valley  “  <x”  behind  the  posterior  ridge  is  introduced 
(Fig.  164). 

The  simplicity  of  the  pattern  is  also  departed  from  by 
the  margins  of  the  ridges,  and  therefore  the  boundaries  of 
the  depressions,  being  waved  and  irregular. 

The  lower  molars  of  the  Rhinoceros  are  made  up  of  two 
crescentic  ridges,  one  in  front  of  the  other,  with  the  hollows 
turned  inwards.  It  is  less  obvious  how  this  pattern  is 

Fig.  164  (J). 


derived  from  that  of  the  Tapir,  but  it  maybe  that  the  trans¬ 
verse  ridges  of  the  Tapir  type  of  tooth  may  have  become 
curved  and  crescentic,  so  that  the  original  outer  edge  of  the 
posterior  ridge  abuts  against  the  back  and  the  exterior  of 
the  ridge  in  front  of  it.  The  valleys  between  the  processes 
of  enamel  and  dentine  of  the  tooth  of  the  Rhinoceros,  termed 
“  sinuses,”  are  not  filled  up  solidly  with  cementum. 

The  Palseotherium  type  of  tooth  may  be  said  to  be 
arrived  at  by  the  outer  wall  becoming  zigzag,  being  bent 
inwards  opposite  to  the  cusps,  and  outwards  at  the 
corners  of  the  tooth  and  opposite  to  the  interspaces  between 
the  cusps.  The  more  complex  pattern  which  characterises 

(l)  Grinding  surfaces  of  upper  molar  series  of  a  Rhinoceros,  a.  Posterior 
sinus,  which  at  a  has  become  an  island,  c.  Posterior  ridge,  d.  Anterior 
ridge. 


392 


A  MANUAL  OF  DENTAL  ANATOMY. 


the  molar  of  the  Horse  may  he  derived  from  a  further 
modification  of  the  Rhinoceros  molar. 

To  use  the  words  of  Professor  Huxley  :  “  Deepen  the 
valley,  increase  the  curvature  of  the  (outer)  wall  and  laminse 
(transverse  ridges),  give  the  latter  a  more  directly  backward 
slope ;  cause  them  to  develop  accessory  ridges  and  pillars  : 
and  the  upper  molar  of  the  Tapir  will  pass  through  the 
structure  of  that  of  the  Rhinoceros  to  that  of  the  Horse.’ ' 

By  a  further  increase  in  the  obliquity  of  the  ridges  and 


Fig.  165  0). 


in  their  curvature  (c  and  d ),  they  become  parallel  to  the 
external  or  antero-posterior  ridge  (wall),  and  bend  round 
until  they  again  touch  it,  thus  arching  round  and  completely 
encircling  the  sinuses  (a  and  the  space  between  c  and  d )  in 
the  Rhinoceros  tooth.  In  this  way  the  unsymmetrical  pattern 
of  the  Rhinoceros  tooth  may  be  supposed  to  become  trans¬ 
formed  into  the  comparatively  symmetrical  one  of  the  Horse 
or  of  the  ruminant. 

The  outer  ridge  or  wall  is  in  the  upper  molar  of  the  horse 
doubly  bent,  the  concavities  looking  outwards.  The  trans¬ 
verse  ridges  start  inwards  from  its  anterior  end  and  from  its 
middle,  and  they  curve  backwards  as  they  go  to  such  an 
extent  as  to  include  crescentic  spaces  (between  themselves 
and  the  outer  wall).  To  this  we  must  add  a  vertical  pillar, 

(!)  Molar  tooth  of  Horse,  showing  the  characteristic  pattern  of  its 
grinding  surface. 


THE  TEETH  OF  PERIS  SOT)  A  CTYLE  VNGVLATA.  383 


which  is  slightly  connected  with  the  posterior  end  of  each 
crescentic  edge  (this  pillar  is  in  Hipparion  quite  detached). 

The  lower  molars  of  the  horse  present  the  double  crescent, 
just  like  those  of  the  rhinoceros,  save  that  vertical  pillars 
are  attached  to  the  posterior  end  of  each  crescent,  thus 
slightly  complicating  the  pattern  of  the  worn  surface.  The 
interspaces  of  the  ridges  and  pillar  are  in  the  horse  solidly 
filled  in  with  cementum.  The  extinct  ancestors  of  the  horse 
are  now,  however,  pretty  well  known,  thanks  to  the  researches 
particularly  of  Prof.  Marsh ;  starting  with  the  Eohippus,  no 
larger  than  a  fox,  with  four  well-developed  toes  and  a  rudiment 
of  the  fifth  (forefoot),  through  the  Eocene  Orohippus  (4-toed), 
the  Miocene  Mesohippus  as  large  as  a  sheep  (3-toed,  with  rudi¬ 
mentary  splint),  the  Upper  Miocene  Miohippus  (3-toed),  the 
Lower  Pliocene  Protohippus,  as  large  as  an  ass  (3-toed,  but 
only  the  middle  one  reaching  the  ground),  which  was  like  the 
European  Hipparion,  and  the  Pliocene  Pliohippus,  which  has 
lost  the  small  hooflets,  whilst  in  the  Upper  Pliocene  the  true 
Equus  first  appears. 

Eohippus  had  forty-four  teeth,  the  molars  being  quite 
distinct  from  the  premolars,  with  short  crowns  and  roots ; 1 
in  Orohippus  the  last  premolar  is  like  the  true  molars,  while 
in  Mesohippus  two  premolars  are  like  the  true  molars. 

The  other  characters  of  the  teeth  are  shown  in  the  diagram 
better  than  they  can  be  conveyed  in  words. 

If  we  had  specimens  of  most  of  the  Ungulates  which  ever 
lived,  there  would  be  no  doubt  as  to  the  relationship  of  the 
various  patterns  :  as  it  is,  we  are  embarrassed  by  the  lack  of 
the  material,  which  leaves  gaps  too  great  to  bridge  over 
without  some  amount  of  speculation.  As  it  is,  Professor 
Flower  divides  the  principal  varieties  of  ungulate  molars 
(Phil.  Trans.,  1874)  into  three  : — 

(i.)  That  in  which  the  outer  wall  is  feebly  developed, 


(b  Ancient  deer  also  liad  short  crowns  to  their  molar  teeth. 


394 


A  MANUAL  OF  DENTAL  ANATOMY. 


Fig.  166  (!). 


Recent. 
Eg  mis. 


o 


Pliocene. 

Pliohippus. 


O 


Protoliippus 
( Hipparion ). 


Mesohippus. 


Eocene. 

Orohippus. 


The  Forefoot  and  surfaces  of  upper  and  lower  molars, 


THE  TEETH  OF  PERIS  SOD  A  CT  YLE  UNGULATA.  395 


and  transverse  ridges  become  the  prominent  features,  as  in 
the  tapir. 

(ii.)  That  in  which  the  outer  wall  is  greatly  developed 
and  more  or  less  smooth,  the  transverse  ridges  being  oblique, 
as  in  the  rhinoceros. 

(iii.)  That  in  which  the  outer  surface  and  edge  of  the 
outer  wall  is  zigzagged,  or  bicrescentic,  as  in  the  horse  and 
palseotherium. 

Equus. — The  horse  is  furnished  with  the  full  mammalian 
number  of  teeth,  the  dental  formula  being — 


I  The  canines,  however,  are  rudimentary  in  the  female,  whilst 
I  in  the  male  they  are  well  developed  (in  the  gelding  they  are 
of  the  same  size  as  in  the  entire  horse) ;  and  the  first  pre¬ 
molar,  which  has  no  predecessor,  is  also  rudimentary,  and  is 


Fig.  167  (')• 


lost  early.  A  considerable  interval  exists  between  the 
incisors  and  the  premolars  and  molars,  which  latter  are  very 
similar  to  one  another,  both  in  shape,  size,  and  in  the 
pattern  of  the  grinding  surface. 

Mares  occasionally  have  all  four  canines,  but  more 
commonly  they  have  only  the  lower  ones. 

The  incisors  of  the  horse  are  large,  strong  teeth,  set  in 
close  contact  with  one  another ;  the  teeth  of  the  upper  and 
lower  jaws  meet  with  an  “edge  to  edge  bite,”  an  arrange- 

(*)  Apex  of  crown  of  an  upper  incisoi  of  a  Horse,  not  yet  completely 
formed. 


396 


A  MANUAL  OF  DENTAL  ANATOMY. 


ment  which,  while  it  is  eminently  adapted  for  grazing,  leads 
to  great  wearing  down  of  the  crowns.  An  incisor  of  a  horse 
or  other  animal  of  the  genus  may  be  at  once  recognized  by 
that  peculiarity  which  is  known  as  the  “  mark.” 

From  the  grinding  surface  of  the  crown  there  dips  in  a 
deep  fold  of  enamel,  forming  a  cut  de  sac.  As  this  pit  does 
not  extend  the  whole  depth  of  the  crown,  and  the  incisors 


Fig.  168  (*).  Fig.  169  (».) 


of  a  horse  are  submitted  to  severe  wear,  the  fold  eventually 
gets  worn  away  entirely,  and  the  worn  surface  of  the  dentine 
termed  the  “ table”  presents  no  great  peculiarity.  But  as 
this  wearing  down  of  the  crown  takes  place  at  something  like 
a  regular  rate,  horse  dealers  are  enabled  to  judge  of  a  horse’s 
age  by  the  appearance  ot  the  mark  upon  the  different  incisors. 
The  “mark”  exists  in  Hipparion,  but  not  in  the  earlier 
progenitors  of  the  horse. 

(  )  Incisors  of  the  Hoise,  showing  the  marks  at  various  stages  of  wear 


THE  TEETH  OF  PERISSODACTYLE  UNGULATA.  397 


A  horse  attains  to  its  adult  dentition  very  slowly.  A  foal 
is  born  with  the  two  central  incisors  in  each  jaw  ;  when 
nine  weeks  old  it  has  four. 

At  2|  years  the  temporary  central  incisors  are  shed,  at  3| 
the  lateral,  and  at  the  corner  incisors,  and  at  5  years  the 
horse  is  said  to  have  a  “  full  mouth.”  As  the  rate  of  wear 


Fig.  170  0). 


is  equal  the  mark  gets  worn  out  sooner  upon  the  central 
incisors,  and  last  upon  the  corner  teeth. 

At  six  the  age  is  judged  of  chiefly  by  the  wear  of  the 
corner  teeth,  as  the  cavity  in  centrals  is  nearly  worn  out,  and 
the  “  table  ”  nearly  complete  on  the  corner  teeth.  At  the 
eighth  year  the  central  table  is  rather  triangular,  while  from 
8  to  10  years  the  small  circle  remains  on  centrals,  and  a 
round  ring  of  enamel  on  corner  teeth. 

After  12  years  the  mark  has  wholly  gone  from  centrals, 
and  there  is  no  certainty  as  to  age. 

fl)  Side  view  of  the  dentition  of  a  Stallion.  At  a  short  interval  behind 
the  incisors  are  seen  the  canines ;  then,  after  a  considerable  interval,  the 
premolar  and  molar  series. 


398 


A  MANUAL  OF  DENTAL  ANATOMY. 


After  the  “mark”  is  worn  away  the  centre  of  the  tooth 
is  marked  by  a  difference  of  colour,  due  to  the  presence  of 
secondary  dentine,  into  which  the  remains  of  the  pulp  has 
been  converted. 

While  in  the  normal  dentition  the  horse  has  only  three 
premolars,  yet  a  fourth,  sometimes  called  wolf’s-tooth,  is 
present  at  the  front  of  the  row,  a  remnant  of  the  fuller 
dentition  of  Pakeotherium  and  Hipparion. 

The  molars  of  the  horse  are  remarkable  for  their  great 
length ;  they  do  not  grow  from  persistent  pulps,  but  never¬ 
theless  they  do  go  on  growing  until  a  great  length  of  crown 
of  uniform  diameter  is  made,  subsequently  to  which  the 
short  and  irregular  roots  are  formed.  As  the  upper  working 
surface  of  the  crown  becomes  worn,  the  tooth  rises  bodily  in 
its  socket,  and  when  by  an  accident  its  antagonist  has  been 
lost,  it  rises  far  above  the  level  of  its  neighbours.  This 
elevation  of  the  tooth  takes  place  quite  independently  of 
growth  from  a  persistent  pulp,  and,  in  fact,  happens  after 
the  formation  of  its  roots. 

The  pattern  of  the  horse’s  molar  has  been  already  de¬ 
scribed  ;  it  should  be  added  that  the  last  molar  differs  from 
the  rest  in  its  posterior  moiety  being  less  developed  than  in 
the  other  teeth. 

As  each  ridge  and  each  pillar  of  the  tooth  consists  of  dentine 
bordered  by  enamel,  and  the  arrangement  of  the  ridges  and 
pillars  is  complex ;  as,  moreover,  cementum  fills  up  the  inter¬ 
spaces,  it  will  be  obvious  that  an  efficient  rough  grinding  surface 
will  be  preserved  by  the  unequal  wear  of  the  several  tissues. 

When  a  bit  is  put  into  a  horse’s  mouth  it  rests  in  the 
interval,  or  diastema,  which  exists  between  the  incisors  and 
the  commencement  of  the  molar  series,  and  the  great  con¬ 
venience  of  the  existence  of  such  a  space  has  led  many 
authors  to  assume  that  the  horse  was  moulded  in  accordance 
with  man’s  special  requirements,  so  that  it  might  be  suited 
for  its  subserviency  to  his  wants. 


THE  TEETH  OF  PERISS ODA CT YL E  UNGVLATA.  399 


But  the  wide  diastema  appeared  in  the  remote  ancestors 
of  the  horse  long  ages  before  man’s  appearance  on  the  earth, 
and  the  advocates  of  this  theory  of  design  would,  as  Professor 
Huxley  suggests,  have  to  tell  us  what  manner  of  animal  rode 
the  Hipparion. 

The  milk  teeth  of  all  the  Ungulata  are  very  complete, 
and  are  retained  late  ;  they  resemble  the  permanent  teeth  in 
general  character,  but  the  canines  of  the  horse,  as  might 
have  been  expected,  their  greater  development  in  the  male 
being  a  sexual  character,  are  rudimentary  in  the  milk 
dentition. 

To  the  Perissodactyle  Ungulates  which  are  specially  inte¬ 
resting  on  account  of  their  dentition,  must  be  added  Homa- 
lodontotherium,  a  tertiary  mammal,  the  remains  of  which 
were  described  by  Professor  Flower  (Phil.  Trans.,  1874). 

It  had  highly  generalised  characters ;  its  teeth  were 
arranged  without  any  diastema,  and  the  transition  in  form 
from  the  front  to  the  back  of  the  mouth  was  exceedingly 
gradual,  so  that  no  tooth  differed  much  from  those  on  either 
side  of  it.  Taking  the  pattern  of  its  molar  teeth  alone  into 
account,  it  would  have  been  without  hesitation  declared  to 
be  very  nearly  allied  to  rhinoceros,  on  which  type  they 
are  formed,  but  the  resemblance  fails  in  the  canine  and 
incisor  region,  and  it  must  be  considered  to  be  one  of  those 
generalised  types  related  to  rhinoceros,  to  Hyracodon  and 
perhaps  connecting  them  with  such  aberrant  forms  as 
Toxodon. 

The  largest  of  Perissodactyles  equalled  the  elephant  in 
size,  and  have  been  named  by  Prof.  Marsh  Bronto'theridse. 
The  dental  formula  was 

2  1  4  3 

1  2  °  I  Pm  3  m  3 

I 

1 

The  incisors  were  small  and  sometimes  deciduous,  and  the 
canines  short  and  stout,  the  lower  being  the  more  conspicuous 


400 


A  MANUAL  OF  DENTAL  ANATOMY. 


owing  to  its  being  separated  by  a  slight  diastema  from  the 
premolars,  which  is  not  the  case  in  the  upper  jaw. 

The  premolars  in  both  jaws  increase  in  size  from  before 
backwards,  and  do  not  differ  from  the  molars  next  them.  In 
the  lower  jaw  the  premolars  and  molars  all  consist  of  two 
crescents,  save  the  last,  which  have  three  crescentic  cusps. 
The  molar  teeth  stand  apart  from  those  of  any  recent  peris  - 
sodactyles  in  their  huge  size,  the  squarish  last  upper  molar, 
for  example,  measuring  four  inches  antero-posteriorly  and 
more  than  three  transversely  (Prof.  Marsh,  American  Journal 
of  Science  and  Arts,  1876). 


THE  TEETH  OF  ARTIODACTYLE  UNGULATA. 

Artiodactyle,  or  even-toed  Ungulata,  comprise  pigs,  hippo¬ 
potami,  camels,  sheep,  oxen,  &c.,  amongst  living  animals. 

They  are  grouped  into 

(i.)  Bunodonts,  or  Suina,  comprising  Pigs  and  Hippo¬ 
potami. 

(ii.)  Selenodonts,  comprising  Anoplotheridse  and  the 
ruminants. 

(a.)  The  Tylopoda  or  Camels. 

(6.)  The  Tragulidee.  Small  deer  of  S.  Asia. 
Chevrotains,  which  are  somewhat  inter¬ 
mediate  between  the  Suidse  and  the  deer. 

(c.)  Pecora,  or  sheep,  oxen,  and  deer. 

The  primitive  Artiodactyla  all  had  forty-four  teeth  of 
brachyodont  type :  in  later  geological  times  they  became 
long-toothed  (hypsodont)  like  recent  sheep  and  oxen. 

Anoplotheridse  are  an  extinct  (Eocene  and  Miocene) 
family,  of  some  what  specialised  character,  and  apparently  not 
on  the  direct  line  of  descent  of  any  modern  forms. 

Anoplotherium  is  a  genus  of  interest  to  the  odontologist 
because  it  possessed  the  full  typical  mammalian  dentition, 


THE  TEETH  OF  ARTIODACTYLE  UNGULATA.  401 


as  far  as  the  number  of  the  teeth  went ;  the  teeth  were 
of  nearly  uniform  height,  none  strongly  differentiated  from 
those  nearest  to  them  ;  and  they  were  set  in  close  contiguity 
with  one  another,  so  that  there  was  no  “  diastema.” 

The  lower  molar  teeth  of  the  Anoplotherium  are  built  up 
on  the  same  type  as  those  of  the  Rhinoceros,  and  present 
the  same  double  crescent :  the  upper  molars  are  also  referable 
tf  the  same  fundamental  forms,  though  the  difference  is 
greater.  The  laminae  (transverse  ridges)  oblique  in  the 

Fig.  171  (J). 


Rhinoceros,  are  in  Anoplotherium  still  more  oblique,  so  that 
they  become  more  nearly  parallel  with  the  outer  wall,  and 
an  accessory  pillar  is  developed  at  the  inside  of  the  anterior 
laminae. 

Not  very  widely  removed  from  Anoplotherium  is  Oreodon, 
an  Ungulate  of  eocene  age. 

Like  a  good  many  tertiary  Ungulates  (both  artiodactyle 
and  perissodactyle)  it  had  the  full  typical  number  of  teeth, 
forty-four  ;  but  its  interest  to  the  cdontologist  is  enhanced 
by  the  co-existence  of  strongly  marked  canines  with  molars 
very  much  like  those  of  ruminants,  a  group  almost  always 
devoid  of  canines. 

In  the  upjDer  jaw  Oreodon  had 

3  1  4  3 

i  — .  c  —  pm  —  m  - — 

f1)  Side  view  of  tlie  dentition  of  Anoplotherium  (after  Owen). 

D  n 


402 


A  MANUAL  OF  DENTAL  ANATOMY. 


i.e .,  the  typical  number  of  each  kind  of  teeth.  But  in  the 
lower  jaw  the  first  four  teeth  are  like  incisors,  and  the 
tooth  which  is  like  a  canine  is  not  the  tooth  corresponding 
to  the  upper  canine,  but  to  the  small  upper  first  premolar. 

This  is  a  fair  illustration  of  the  fact  that  although  in 
nature  it  is  generally  the  same  tooth  which  is  modified  to 
perform  the  function  of  a  canine,  it  is  not  invariably  the 
same  ;  for  here  in  the  same  animal  are  two  different  teeth 
in  the  upper  and  lower  jaws  thus  respectively  modified. 


Fig.  172  f1). 


And  as  they  are  different  teeth,  it  happens  that  the  upper 
(canine)  closes  in  front  of  the  lower. 

There  is  reason  to  believe  that  there  was  some  difference 
in  the  size  of  canines  between  the  male  and  female  Oreodon. 

In  Artiodactyle  Ungulata  the  premolars  differ  markedly 
both  in  size  and  pattern  from  the  true  molars. 

Of  those  Artiodactyle  Ungulates  which  are  not  ruminants 
the  common  pig  may  be  taken  as  an  example. 

The  dental  formula  is  i  —  c  —  p  -  m 

3  1  1  3  3 

The  position  of  the  upper  incisors  is  peculiar,  the  two 
central  upper  incisors,  separated  at  their  bases,  being  inclined 
towards  one  another  so  that  their  apices  are  in  contact ;  the 

0)  Upper  and  lower  teeth  of  Oreodon  Culbertsonii  (after  Leidy,  Smith¬ 
sonian  Contributions,  1852). 


THE  TEETH  OF  ARTIODACTYLE  UNGULATA.  403 


third  pair  are  widely  separated  from  the  inner  two  pairs  of 
incisors.  The  lower  incisors  are  straight,  and  are  implanted 
in  an  almost  horizontal  position :  in  both  upper  and  lowTer 
jaws  the  third  or  outermost  incisors  are  much  smaller  than 
the  others. 

The  lower  incisors  are  peculiar  in  having  upon  their  upper 
surfaces  a  strongly  pronounced  sharp  longitudinal  ridge  of 
enamel,  which  gets  obliterated  by  wear. 

An  interval  separates  the  incisors  from  the  canines,  which 
latter  are  very  much  larger  in  the  male  than  in  the  female, 
and  in  the  wild  boar  than  in  the  domesticated  animal. 
Castration  arrests  the  further  development  of  the  tusks ;  the 
peculiarities  as  to  size  and  direction  which  characterise  the 
tusks  of  the  adidt  animal  are  not  represented  in  the  canines 
of  the  milk  dentition,  about  which  there  is  not  much  that 

4 

is  noteworthy,  save  that  the  young  pig  has  dec.  m  — ,  of 

which  the  first  remains  in  place  till  the  permanent  dentition 
is  nearly  complete,  and  then  falls  out  without  having  any 
successor ;  or  it  may  perhaps  be  regarded  as  a  permanent 
tooth  which  has  had  no  predecessor. 

A  similar  condition  as  to  early  loss  of  the  tooth  immediately 
behind  the  canine  obtains  in  the  Dog  and  in  the  Hippo¬ 
potamus,  their  dental  formulae  being  generally  written  p. 

4 

The  form  and  direction  of  the  canines  are  alike  peculiar ; 
the  upper  canine,  which  in  its  curvature  describes  more 
than  a  semicircle,  leaves  its  socket  in  a  nearly  horizontal 
direction,  with  an  inclination  forwards  and  outwards.  After 
rounding  past  the  upper  lip  its  terminal  point  is  directed 
upwards  and  inwards.  The  enamel  upon  the  low'er  surface 
of  the  tusk  is  deeply  ribbed :  it  does  not  uniformly  cover  the 
tooth,  but  is  disposed  in  three  bands.  The  lower  canines 
are  more  slender,  of  much  greater  length,  and  by  wear 
become  more  sharply  pointed  than  the  upper  ones :  they 

n  d  2 


404 


A  MANUAL  OF  DENTAL  ANATOMY. 


pass  in  front  of  the  latter,  and  the  worn  faces  of  the  two 
correspond. 

The  lower  canine  is  in  section  triangular,  one  edge  being 
directed  forwards,  and  its  sides  being  nearly  flat.  Enamel 
is  confined  to  the  internal  and  external  anterior  surfaces ; 
the  posterior  surface,  which  plays  against  the  upper  canine,  is 
devoid  of  enamel,  and  the  tooth  is  kept  constantly  pointed  by 
the  obliquity  with  which  its  posterior  surface  is  worn  away. 
The  tusks  of  a  boar  are  most  formidable  weapons,  and  are 


Fig.  173  (*). 


capable  of  disembowelling  a  dog  at  a  single  stroke,  but  they 
are  greatly  exceeded  by  those  of  the  African  Wart-hog 
Phacochoerus),  which  attain  to  an  immense  size. 

In  the  domestic  races  the  tusks  of  the  boars  are  much 
smaller  than  in  the  wild  animal,  and  it  is  a  curious  fact 
that,  in  domestic  races  which  have  again  become  wild  the 
tusks  of  the  boars  increase  in  size,  at  the  same  time  that 
the  bristles  become  more  strongly  pronounced.  Mr.  Darwin 
suggests  that  the  renewed  growth  of  the  teeth  may  perhaps 
be  accounted  for  on  the  principle  of  correlation  of  growth, 
external  agencies  acting  upon  the  skin,  and  so  indirectly 
influencing  the  teeth. 

As  in  most  Artiodactyles,  the  teeth  of  the  molar  series 

0)  Upper  and  lower  teeth  of  Wild  Boar  (Sus  scrofa).  In  this  specimen 
the  tusks  are  not  so  largely  developed  as  they  sometimes  may  be  seen  to  be. 


THE  TEETH  OF  ART  I OH  A  CTYLE  UNGULATA.  405 


increase  in  size  from  before  backwards  :  thus  the  first  pre¬ 
molar  ( ?  milk  molar)  has  a  simple  wedge-shaped  crown,  and 
two  roots  ;  the  second  and  third  by  transitional  characters 
lead  to  the  fourth  premolar,  which  has  a  broad  crown  with 
two  principal  cusps,  and  has  four  roots. 

The  first  true  molar  has  four  cusps  divided  from  one  another 
by  a  crucial  depression ;  and  the  cingulum  in  front,  and  yet 
more  markedly  at  the  back,  is  elevated  into  a  posterior  trans¬ 
verse  ridge.  In  the  second  molar  the  transverse  ridge  is  more 
strongly  developed,  and  the  four  cusps  are  themselves  some¬ 
what  divided  up  into  smaller  accessory  tubercles. 

The  last  molar  measures,  from  front  to  back,  nearly  twice  as 
much  as  the  second;  and  this  great  increase  in  size  is  referable 
to  a  great  development  of  the  part  corresponding  to  the 
posterior  ridge  or  cingulum  of  the  second  molar,  which  has 
become  transformed  into  a  great  many  subsidiary  tubercles. 

That  such  is  a  correct  interpretation  of  its  nature  is  indi¬ 
cated  by  our  being  able  to  trace  the  four  principal  cusps, 
though  modified  and  not  divided  off,  in  the  front  part  of  the 
tooth,  of  which,  however,  they  do  not  constitute  more  than 
a  small  part.  Those  Ungulates  in  which  the  surfaces  of  the 
molar  teeth  are  covered  by  rounded  or  conical  cusps,  are 
termed  “  bunodonts,”  in  contradistinction  to  those  which 
present  crescentic  ridges  on  the  masticating  surface  of  their 
molars,  and  which  go  by  the  name  of  “  selenodonts.” 

In  the  Wart-hog  (Phacochoerus),  the  genus  with  very  large 
canines,  the  disproportion  between  the  last  true  molar  and 
the  other  teeth  is  yet  more  striking. 

In  antero-posterior  extent  the  third  molar  equals  the  first 
and  second  true  molars  and  the  third  and  fourth  premolars 
(the  whole  number  of  teeth  of  the  molar  series  possessed  by 
the  animal)  together. 

When  a  little  worn  its  surface  presents  about  thirty  islands 
I  of  dentine,  surrounded  by  rings  of  enamel,  the  interspaces 
and  the  exterior  of  the  whole  being  occupied  by  cementum. 


406 


A  MANUAL  OF  DENTAL  ANATOMY. 


Of  course,  prior  to  the  commencement  of  wear,  each  of  these 
islands  was  an  enamel-coated  cusp. 

The  Wart-hog’s  dentition  has,  however,  another  instructive 
peculiarity ;  the  first  true  molar  is  in  place  early,  and  be¬ 
comes  much  worn  down  (this  is  true,  in  a  less  degree,  of  the 
common  pig,  and  indeed  of  most  Ungulata).  Eventually  it 


is  actually  shed ;  the  same  fate  later  befalls  the  third  pre¬ 
molar  and  second  true  molar,  so  that  the  dentition  in  an 
aged  specimen  is  reduced  to  the  fourth  premolar  and  the 
third  true  molar  alone,  and  eventually  to  the  last  true 
molars  alone.  Thus,  both  in  the  great  complexity  of  the 
back  molars  and  the  fact  that  the  anterior  teeth  are  worn 
out  and  then  discarded,  the  Wart-hog  affords  a  parallel  to 
the  anomalous  dentition  of  the  elephant. 

f1)  Upper  and  lower  teeth  of  Pliacochoerus.  In  the  upper  jaw,  the  last 
two  premolars,  and  the  much-worn  first  true  molar  remain.  In  the  lower 
all  have  been  shed  off,  save  the  last  two  true  molars.  From  a  specimen 
in  the  Museum  of  the  Royal  College  of  Surgeons. 


THE  TEETH  OF  ARTIODACTYLE  UNOULATA.  407 


As  has  already  been  noticed,  the  upper  canines  in  the 
boar  turn  outwards  and  finally  upwards,  so  as  to  pass  out¬ 
side  the  upper  lip ;  this  peculiarity  in  direction,  yet  more 
marked  in  Phacochoerus,  attains  its  maximum  in  the  Sus 
babirussa. 

This  creature,  strictly  confined  to  the  Malay  Archipelago, 
where  it  frequents  woody  places,  has  (in  the  male)  the  upper 
and  lower  canines  developed  to  an  enormous  extent.  The 
upper  canines  are  turned  upwards  so  abruptly  that  they 


Fig.  175  (l). 


pierce  the  upper  lip,  instead  of  passing  outside  it  as  in  other 
Suidse,  preserve  a  nearly  upright  direction  for  some  little 
distance,  and  then  curve  backwards,  so  that  their  points  are 
directed  almost  towards  the  eyes. 

The  lower  canines  are  less  aberrant  in  direction  and  in 
shape,  being  somewhat  triangular  in  section,  but  they  also  are 
of  very  great  length,  and  pass  upwards,  far  above  the  level 

(!)  Skull  of  Sus  babirussa  (male).  The  upper  incisors  have  been  lost 
from  the  specimen  figured  :  they  are  much  like  those  of  a  pig. 


408 


A  MANUAL  OF  DENTAL  ANATOMY. 


of  the  snout ;  tlieir  points  are  also  directed  backwards,  but 
have  in  addition  an  outward  inclination.  The  canines  are 
devoid  of  enamel,  and  grow  from  persistent  pulps,  a  fact 
which  sometimes  has  a  disastrous  result,  for  the  tip  of  the 
tooth,  occasionally  taking  a  wrong  direction,  re-enters  the 
head  or  the  jaws  of  the  animal. 

Their  length  is  very  great ;  the  animal  is  smaller  than  the 
domesticated  pig,  but  its  canines  attain  a  length  of  eight  or 
ten  inches.  Their  use  is  a  matter  of  conjecture;  the  position 
of  the  upper  tusks  has  suggested  the  idea  that  they  may 
serve  as  a  protection  to  the  creature’s  eyes,  as  it  seeks  its 
food,  consisting  of  fallen  fruits,  amongst  the  brushwood.  But 
were  that  the  case  the  female  also  would  probably  have 
them,  which  is  not  the  case,  the  upper  canine  being  only 
about  f  inch  long,  though  it  is  everted  and  is  beginning  to 
turn  upwards  ;  the  lower  tooth  is  a  little  larger;  and  although 
in  old  animals  they  are  often  broken  off,  it  is  not  certain  that 
•  they  are  much  employed  in  fighting.  Its  other  teeth  are  in 
no  respects  remarkable. 

Hippopotamus. — The  dental  characters,  as  well  as  others, 
indicate  the  affinity  of  the  Hippopotamus  to  the  Suida3. 


The  incisors  are  tusk-like,  and  bear  but  little  resemblance  to 
those  of  most  other  mammalia ;  they  are  nearly  cylindrical, 
bluntly  pointed  at  their  apices  by  the  direction  of  weai;, 
and  this  is  in  some  measure  determined  by  the  partial  distri¬ 
bution  of  the  enamel,  which  is  laid  on  in  longitudinal  bands 
in  the  upper  teeth,  but  merely  forms  a  terminal  cap  on  the 
lower  incisors. 

The  upper,  standing  widely  apart,  are  implanted  nearly 
vertically  :  the  lower  incisors,  of  which  the  median  pair  are 
exceedingly  large,  are  implanted  horizontally. 

The  canines  are  enormous  teeth ;  the  lower,  as  in  the  Hog, 


THE  TEETH  OF  ARTIODACTYLE  UNGULATA.  409 


are  trihedral,  and  are  kept  pointed  in  the  same  manner ;  the 
upper  canines  are  not  so  long,  and  the  portion  exposed  above 
the  gum  is  relatively  short. 

The  incisors  and  canines  are  all  alike  teeth  of  persistent 
growth. 

The  premolars,  of  which  the  first  is  lost  early  (being,  like 
the  similar  tooth  in  the  pig,  perhaps  a  milk  molar)  are 
smaller  and  simpler  teeth  built  up  on  the  same  type  as  the 
true  molars. 

These  latter,  especially  when  worn,  have  a  very  character¬ 
istic  double  trefoil  pattern  ;  the  four  cusps,  in  the  first  in¬ 
stance,  were  separated  by  a  deep  longitudinal  and  a  still 
deeper  transverse  groove  ;  each  cusp  was,  moreover,  trilobed; 
the  first  result  of  wear  is  to  bring  out  the  appearance  of 
four  trefoils ;  next,  when  the  longitudinal  furrow  is  worn 
away,  two  four-lobed  figures  result ;  and  finally  all  pattern 
becomes  obliterated,  and  a  plain  field  of  dentine  surrounded 

bv  enamel  alone  remains. 

%/ 

The  teeth  of  the  Hippopotamus  are  subject  to  a  great 
amount  of  attrition,  as  is  well  shown  by  a  specimen  pre¬ 
sented  to  the  Museum  of  the  Odontological  Society,  in  which 
the  molar  teeth  are  all  excessively  worn.  The  Hippopotami 
use  their  incisors  and  canine  tusks  for  the  purpose  of  up¬ 
rooting  aquatic  plants,  of  which  their  food  mainly  consists  : 
the  roots  of  these  are  of  course  mixed  up  with  much  sand, 
which  wears  down  the  teeth  with  great  rapidity.  The  larger 
incisors  and  the  canines  are,  and  for  centuries  have  been, 
articles  of  commerce,  the  ivory  being  of  very  dense  substance 
and  useful  for  the  manufacture  of  small  objects. 

The  remaining  Selenodont  Ungulates  are  divided  into  the 
Tylopoda  (Camels),  the  Tragulina  and  Pecora. 

The  Camels  have  both  upper  incisors  and  canines,  the 

dental  formula  being  : — 

.113  3 

i  _  c  —  p  -  m 


410 


A  MANUAL  OF  DENTAL  ANATOMY. 


The  first  two  pairs  of  upper  incisors  are  absent,  but  the 
third  or  outermost  pairs  are  present,  and  are  rather  caniniform 
in  shape.  In  quite  young  skulls  six  upper  incisors  are  pre- 

Fig.  176  (>). 


sent,  but  the  two  inner  pairs  are  lost  very  early.  The 
canines  are  strong  pointed  teeth,  and  the  lower  canine 

Fig.  177  (2). 


stands  well  apart  from  the  three  incisors  of  the  lower  jaw 
unlike  the  fourth  tooth  in  front  of  the  mandible  of  typical 
pecora  (see  Fig.  178). 

The  first  premolars  are  absent  altogether ;  the  second  pre¬ 
molars,  following  the  canines  after  an  interval,  are  pointed 

caniniform  teeth.  The  third  premolar  is  sometimes  lost 
early,  but  the  fourth  persists. 

The  molars  of  the  Camel  are  of  the  “  Selenodont  ”  type ; 


(!)  Upper  and  lower  teeth  of  a  Camel. 
(  )  Selenodont  molar  of  a  deer. 


THE  TEETH  OF  ARTIODA CTYLE  UNGTJLATA.  411 


their  derivation  from  forms  already  alluded  to  will  be 
sufficiently  obvious  to  the  reader  who  has  mastered  the 
descriptions,  and  their  double  crescentic  crowns,  may 
be  taken  as  fair  examples  of  simple  ruminant  patterns, 
accessory  pillars,  &c.,  being  added  in  some  of  the  other 
families. 

The  Tragulina  or  Chevrotains,  sometimes  called  Pigmy 
Musk  Deer,  though  somewhat  intermediate  between  the  Pigs 
and  Deer,  and  zoologically  distinct  enough,  do  not  differ  in 
their  dentition  from  the  true  ruminants,  with  which  they 
may  be  noticed  here. 

The  hollow-horned  ruminants  (sheep  and  oxen  and  ante¬ 
lopes),  and  likewise  almost  all  the  solid  horned  ruminants 
(deer)  have  the  following  dental  formula : — 

.00  133 

l  —  c—  or  c  - p  —  m  — 

31  l1  3  3 

The  lower  incisors  are  antagonised  not  by  teeth,  but  by 
a  dense  gum  which  clothes  the  fore  part  of  the  upper  jaw ; 
if  a  sheep  is  watched  as  it  feeds,  it  will  be  seen  to  grasp  the 
blades  of  grass  between  the  lower  teeth  and  the  gum,  and 
then  to  tear  them  off  by  an  abrupt  movement  of  the  head, 
as  it  would  be  impossible  for  it  to,  strictly  speaking,  bite 
it  off. 

The  anomaly  of  the  entire  absence  of  upper  incisors  wras 
held  to  have  been  diminished  by  the  statement  of  Goodsir, 
who  believed  that  uncalcified  tooth  germs  were  to  be 
found  in  the  foetuses  of  many  species.  ( As  this  was  precisely 
what  might  have  been  expected,  it  has  since  that  time 
passed  current  as  an  established  fact ;  but  M.  Pietkewickz, 
working  in  the  laboratory  of  M.  Ch.  Robin,  has  absolutely 
denied  the  occurrence  of  even  the  earliest  rudiments  of 
tooth  germs  in  this  situation,  after  an  examination  of  a 
series  of  foetuses  of  the  sheep  and  cow,  ranging  even 
from  the  earliest  periods.  (Journal  d’Anatomie,  par  C.  H. 


412 


A  MANUAL  OF  DENTAL  ANATOMY. 


Eobin,  1873,  p.  452.)  Since  meeting  with  this  statement 
I  have  had  no  opportunity  of  verifying  this  matter 
myself. 

Grouped  with  the  six  incisors  of  the  lower  jaw,  and  in  no 
respect  differing  from  them,  rise  the  pair  of  teeth  which  are 
very  arbitrarily  termed  “  canines.”  As  I  cannot  attempt  to 
do  more  in  these  pages  than  give  the  most  bare  outline  of 
generally  well-known  facts,  I  have  retained  the  usual  dental 


formula,  i  - 
•  • 


0 


;  though  under  protest,  as  I  do  not  con¬ 


sider  the  “  canine  ”  to  have  any  such  distinct  existence  as 
would  justify  our  calling  a  tooth  which  is  so  obviously  refer¬ 
able  to  the  incisors  by  any  distinctive  name. 

Although  the  absence  of  upper  canine  teeth  is  a  very 
general  characteristic  of  ruminants,  rudimentary  canines 
exist  in  some  deer,  and  I  am  indebted  to  the  kindness  of 
Sir  Victor  Brooke,  a  high  authority  upon  the  Cervidce,  for 
the  following : — 

“  The  upper  canines  are  present  in  both  sexes  in  all  the 
species  of  Cervidce,  with  the  exception  of  Alces,  Eangifer, 
Dama,  some  smaller  species  of  Kusa,  Axis,  Capreolus,  Caria- 
cus,  Blastocerus,  Coassus,  and  Pudu.  The  upper  canines, 
when  present,  are  with  the  notable  exception  of  Moschus, 
Elaphodus,  Cervulus,  and  Hydropotes,  small  laterally  com¬ 
pressed  rudimentary  teeth.  Their  crowns  are  in  about  the 
same  stage  of  reduction  as  the  crowns  of  horses’  canines, 
but  their  roots  are  relatively  much  more  reduced.”  Hence 
they  are  often  lost  in  dried  skulls,  and  it  has  generally  been 
supposed  that  but  few  deer  possessed  canines  at  all. 

The  hornless  musk  deer  possesses  upper  canines  of  most 
formidable  dimensions,  while  the  female  has  very  small 
subcylindrical  canines. 

The  male  pigmy  musk  deer  (Tragulus)  has  large  canines 
of  persistent  growth,  the  female  small  canines  with  closed 
roots. 


THE  TEETH  OF  ARTIODACTYLE  UNGULATA .  4]  3 


The  Indian  Muntjac  deer  (Cervulus)  has  somewhat  small 
horns,  which  are  perched  upon  persistent  bony  pedicles, 
and  it  has  upper  canines  which  are  curved  outwards  from 
beneath  the  upper  lip,  much  as  are  the  tusks  of  a  boar ; 
they  do  not,  however,  grow  from  persistent  pulps,  and  are 
absent  in  the  female. 


Fig.  178  0). 


Cuvier  first  pointed  out  that  there  was  a  relation  between 
the  presence  of  horns  and  the  absence  of  canine  teeth ;  the 
latter,  serving  as  weapons  for  sexual  combat  solely,  and 
being,  probably,  in  no  other  wray  of  service  to  the  animal, 
are  not  required  by  an  animal  provided  vdth  powerful  antlers 
or  horns,  whereas  the  absolutely  hornless  musk  deer  would 
be  totally  unprovided  wfith  weapons  of  offence  w^ere  it  not  for 
his  canines.  To  the  musk  deer  and  the  muntjac  must  be 
added  Swinhoe’s  water  deer,  Hydropotes  inermis,  which  has 
canines  shorter  and  stouter  than  Mosclius,  and  Michie’s  deer, 
Elaphodus  cephalopus,  another  small  hornless  species,  of 
which  the  males  are  furnished  with  formidable  canine  teeth, 
which  are  not  so  long  as  those  of  Moschus,  but  are  flattened 
from  side  to  side,  and  are  very  strong. 


(i)  Cranium  of  male  Musk  deer  (Mosclius  moscliiferus). 


414 


A  MANUAL  OF  DENTAL  ANATOMY. 


Although,  with  the  foregoing  exceptions,  all  the  deer, 
oxen,  sheep,  antelopes,  and  the  giraffe,  animals  constituting 
the  greater  number  of  the  “  Ruminantia,”  are  without 
canine  teeth,  yet  in  the  Camelidse,  tusk-like  canines  are 
met  with. 

It  is  a  character  of  the  Artiodactyle  Ungulata  that  the 
premolar  teeth  are  of  decidedly  simpler  form  than  the 
molars  :  in  the  ruminants  the  premolars  may  be  said  each 
to  roughly  correspond  to  one  half  of  a  true  molar,  and  the 
premolars  and  molars  form  a  continuous  series. 

In  all  true  Ruminants  the  last  true  molar  of  the  lower 
jaw  has  a  third  lobe  (!),  and  the  line  of  the  outer  surface 
of  the  row  of  teeth  is  rendered  irregular  by  the  anterior 
edge  of  each  tooth  projecting  outwards  slightly  more 
than  the  posterior  border  of  the  one  in  front  of  it.  And 
the  deviations  in  the  patterns  of  the  surfaces  of  the  molar 
teeth  are  so  constant  and  so  characteristic  that,  although 
the  common  ruminant  pattern  is  preserved  in  all,  it  is 
often  possible  to  refer  an  individual  tooth  to  its  right 
genus. 

The  Ruminants  all  have  a  wTell-developed  milk  dentition, 
which  serves  the  animal  for  a  long  time,  indeed  until  after 
it  has  attained  to  its  adult  dimensions  ;  thus  a  sheep  has  not 
completed  the  changing  of  its  teeth  till  the  fifth  year,  and 
a  calf  till  the  fourth  year.  But  the  first  permanent  molar 
is  in  them,  as  in  so  many  other  animals,  the  first  of  the 
permanent  set  to  be  cut,  and  comes  up  in  its  place  at  the 
sixth  month  (in  the  lamb),  and  hence  has  a  long  j>eriod 
of  wear  before  any  of  the  other  second  teeth  are  cut. 
Consequently  the  first  permanent  molar  is,  as  is  seen  in 
Fig.  176,  invariably  worn  down  to  a  much  greater  extent  than 
the  other  permanent  teeth ;  in  the  specimen  figured  it  has 
been  worn  down  below  the  inflections  of  enamel,  so  that  it 

P)  Sir  Victor  Brooke  informs  me  that  Neotragus  liemprichii,  a  small 
Abyssinian  antelope,  has  only  two  lobes  to  the  third  lower  molar. 


TOXODONTIA. 


415 


has  lost  its  roughened  grinding  surface,  and  is  reduced  to  a 
smooth  area  of  dentine. 

Not  much  is  known  of  the  structure  of  the  dental  tissues 
of  the  Ungulata  calling  for  mention  in  an  elementary  work. 
The  thick  cement  of  the  crown  of  the  teeth  of  the  Horse, 
and  indeed  of  most  of  the  group  which  possess  thick  cement, 
contains  many  “  encapsuled  lacunae,”  and  is  developed  from 
a  distinct  cement  organ  of  cartilaginous  consistence. 


AMBLYPODA. 

The  Polydactyle  Ungulates  form  an  ill-defined  group,  to 
which  Hyrax  and  Proboscidea  may  be  referred,  as  well  as  a 
number  of  extinct  forms,  mostly  American,  the  exact 
affinities  of  which  remain  uncertain. 


TOXODONTIA. 

The  existing  ungulate  animals  form  onl;y  a  small  proportion 
of  those  once  peopling  the  earth,  and  many  extinct  forms 
have  been  discovered,  which  while  forming  affinities  with  the 
Ungulata,  can  yet  hardly  be  classified  under  any  existing 
order.  For  example,  Toxodon,  a  creature  equalling  the 
Hippopotamus  in  size,  which  was  discovered  by  Mr.  Darwin 
in  late  tertiary  deposits  of  South  America,  has  a  dentition 
recalling  in  some  respects  the  Bruta,  in  others  the  Kodents. 

Its  dental  formula  was 

.2  0  4  3 

i-C  —  p  —  m— . 

2  1  1  3  3 

It  possessed  in  the  upper  jaw  two  pairs  of  incisors,  the 


416 


A  MANUAL  OF  DENTAL  ANATOMY. 


median  pair  small,  the  outer  exceedingly  large,  with  per¬ 
sistent  pulps,  and  long  curved  sockets  extending  back  to  the 
region  of  the  molars,  just  as  in  existing  Rodents. 

In  the  lower  jaw  there  were  three  pairs  of  incisors,  sub¬ 
equal  in  size,  and  growing  from  persistent  pulps ;  they 
resemble  the  incisors  of  Rodents  in  having  a  partial  invest¬ 
ment  with  enamel,  but  differ  from  them  in  being  prismatic 
in  section,  and  in  having  the  enamel  disposed  on  two  sides 
of  the  prism. 

The  molars  were  also  very  remarkable  ;  they  grew  from 
persistent  pulps,  and  had  curved  sockets,  but  the  curvature 
of  these  was  in  the  reverse  direction  to  that  which  obtains 
in  Rodents,  i.e.,  the  convexity  was  outwards,  and  the  apices 
of  their  roots  almost  met  in  the  middle  line  of  the  palate ;  it 
was  this  peculiarity  that  suggested  the  name. 

Another  peculiarity  in  the  molar  teeth,  in  which  they 
stand  quite  alone,  is  that,  like  incisors,  they  have  a  partial 
investment  with  enamel ;  those  referred  to  the  premolar 
series  having  it  confined  to  their  outer  surfaces,  while  the 
three  back  teeth  of  the  molar  series  had  a  plate  also  laid  on 
to  their  inner  surfaces  ;  there  were  seven  back  teeth  above, 
and  six  below. 

In  the  interval  between  the  incisor  and  molar  series 
canines  have  been  found  in  the  lower  jaw;  they  were  sharp 
edged,  and  had  a  partial  distribution  of  enamel  over  their 
surface.  In  an  upper  jaw  alveoli  for  canines  were  found,  but 
the  teeth  themselves  are  not  known. 

Another  animal  from  the  same  locality  (Mesotherium) 
had  somewhat  similar  characters,  though  it  was  not  nearly 
so  large  :  it  had 


0  2  3 

c0  pmlm3 


the  incisors  (of  persistent  growth)  standing  apart  from  the 
premolar  and  molar  series  just  as  in  the  Rodents. 


DINOCERATA. 


417 


DINOCERATA. 


In  the  same  region  which  yielded  the  toothed  birds 
(Eocene  formations  of  Wyoming),  the  remains  of  many  huge 
animals  have  been  discovered,  for  which  new  orders  have  been 
proposed  by  Prof.  Marsh  (American  Journal  of  Science  and 
Art,  1876),  it  being  impossible  to  classify  them  under  any 
existing  order.  The  Dinocerata  were  creatures  nearly  as 
large  as  elephants,  and  presenting  some  sort  of  resemblance 
to  them  in  general  form ;  they  were  remarkable  for  the 
relative  smallness  of  their  brains,  which  could  apparently 
have  been  drawn  through  the  canal  of  the  vertebral  column. 
They  present  points  of  resemblance  to  the  Perissodactyle 
Ungulata,  and  also  to  the  Proboscidea,  to  which  they  were 
at  first  referred,  though  their  affinities  are  rather  with  the 
former. 

The  dental  formula  was 


1  3 

c  prm  -  m 

1  O 


3 

3' 


In  Prof.  Marsh’s  words,  “  The  superior  canines  are  long, 
decurved,  trenchant  tusks.  They  are  covered  with  enamel, 
and  their  fangs  extend  upwards  into  the  base  of  the  maxil¬ 
lary  horn-core.  There  is  some  evidence  that  these  tusks 
were  smaller  in  the  females.  Behind  the  canines  there  is  a 
moderate  diastema.  The  molar  teeth  are  very  small.  The 
crowns  of  the  superior  molars  are  formed  of  two  transverse 
crests,  separated  externally,  and  meeting  at  their  inner 
extremity.  The  first  true  molar  is  smaller  in  this  specimen 
than  the  two  preceding  premolars.  The  last  upper  molar 

is  much  the  largest  of  the  series. 

y 

“  The  lower  jaw  in  Dinoceras  is  as  remarkable  as  the  skull. 
Its  most  peculiar  features  are  the  posterior  direction  of  the 
j  condyles,  hitherto  unknown  in  Ungulata,  and  a  massive 
decurved  process  on  each  ramus  extending  downward  and 
outward  below  the  diastema. 


E  E 


418 


A  MANUAL  OF  DENTAL  ANATOMY. 


“  The  position  of  the  condyles  was  necessitated  by  the  long 
upper  tusks,  as,  with  the  ordinary  ungulate  articulation,  the 
mouth  could  not  have  been  fully  opened.  The  low  position 
of  the  condyle,  but  little  above  the  line  of  the  teeth,  is  also 
a  noteworthy  character.  The  long  pendant  processes  were 


Fig.  179  0). 


apparently  to  protect  the  tusks,  which  otherwise  would  be 
very  liable  to  be  broken.  Indications  of  similar  processes 
are  seen  in  Smilodon  and  other  Carnivores  with  long  upper 
canines.  With  the  exception  of  these  processes  the  lower 
jaw  of  Dinoceras  is  small  and  slender.  The  symphysis  is 
completely  ossified.  The  six  incisors  were  contiguous,  and 
all  directed  well  forward.  Just  behind  these,  and  not 


(’)  Upper  and  lower  jaws  of  Dinoceras  (Marsh). 


TILL  ODON  TIA .  419 


separated  from  them,  were  the  small  canines,  which  had  a 
similar  direction.  The  crowns  of  the  large  molars  have 
transverse  crests,  and  the  last  of  the  series  is  the  largest.” 

It  would  appear  possible  that  the  eminences  shown  in  the 
figure,  and  spoken  of  as  “maxillary  horn-cores,”  may  be 
merely  the  extended  sockets  of  the  teeth,  which  would  other- 
wise  have  had  an  implantation  inadequate  to  their  length  ; 
they  are,  however,  described  as  solid,  except  at  their  bases, 
where  they  are  perforated  for  the  fang  of  the  canine  tusk, 
which  would  look  as  though  they  were  truly  horn-cores  ; 
moreover  the  Brontotheridae  had  horn-cores  equally  peculiar 
in  position  ( i.e .,  on  the  maxillary  bones). 

Tinoceras,  another  genus,  had  a  very  long  and  slender 
canine,  also  protected,  when  the  mouth  was  closed,  by  a 
downward  prolongation  of  the  lower  jaw  as  in  Dinoceras. 


TTLLODONTIA. 

This,  yet  another  new  order,  comprising  several  genera, 
has  been  proposed  by  Prof.  Marsh  for  Wyoming  fossil  re¬ 
mains,  to  receive  forms  which,  though  not  amongst  the 
biggest,  are  “amongst  the  most  remarkable  yet  discovered  in 
American  strata,  and  seem  to  combine  characters  of  several 
distinct  groups ;  viz.,  Carnivora,  Ungulata,  and  Rodentia.” 
In  Tillotherium,  Marsh,  the  type  of  the  order,  the  skull  has 
the  same  general  form  as  in  the  bear,  but  in  its  structure 
resembles  that  of  the  Ungulata.  Its  molar  teeth  are  of  the 
Ungulate  type,  the  canines  are  small,  and  in  each  jaw  there 
is  a  pair  of  large  scalpriform  incisors,  faced  with  enamel  and 
growing  from  persistent  pulps,  as  in  the  Rodents.  The 
second  pair  of  incisors  are  small,  and  have  not  persistent 
pulps.  The  adult  dentition  is  as  follows — 

.21  33 

i  -  c  -  prm  —  m 
2  1  1  2  3 


E  E  2 


420 


A  MANUAL  OF  DENTAL  ANATOMY. 


“There  are  two  distinct  families,  Tillotheridce  (perhaps 
identical  with  Ancliippodontidce ),  in  which  the  large  incisors 
grew  from  persistent  pulps,  while  the  molars  had  roots ;  and 
the  Stylinodo7itidce,  in  which  all  the  teeth  have  persistent 
pulps.” 

One  genus  (Dryptodon),  known  only  by  the  lower  jaw,  had 
six  teeth,  described  as  “  clearly  incisors,”  the  two  inner  pairs 


Fig.  180(1). 


of  which  are  small  and  cylindrical,  the  outer  of  enormous 
size,  faced  in  front  only  with  enamel,  and  with  persistent 
pulps  carried  back  under  the  premolars. 

Whilst  Prof.  Flower  endorses  Prof.  Marsh’s  view  that 
Tillodonts  have  Ungulate  affinities  and  resemblances  to 
Bodents  also,  this  is  disputed  by  Mr.  Dali  (Amer.  Syst. 
Dental  Surgery,  Art.  Teeth  of  Vertebrates),  who  says  that  he 
fails  to  discover  any  traces  of  Ungulate  relationship,  and 
he  prefers  to  refer  them  to  those  generalised  forms  with  Insec¬ 
tivorous  affinities  which  Prof.  Cope  groups  as  Bunotheria. 
The  adaptive  character  of  incisors  faced  with  enamel  and  of 

Upper  and  lower  jaws  of  Tillotherium  (Marsh). 


THE  TEETH  OF  CARNIVORA. 


421 


persistent  growth  he  would  appear  to  consider  as  not  going 
far  towards  establishing  more  than  a  superficial  resemblance 
to  Rodentia. 

The  pattern  of  its  molar  teeth  is  closely  similar  to  that  of 
Esthonyx  (Cope),  an  Eocene  mammal  with  a  dentition  re¬ 
sembling  that  of  a  gigantic  Shrew. 


THE  TEETH  OF  CARNIVORA. 

The  animals  grouped  together  under  the  name  of 
Carnivora  are  divided  into  two  sections,  the  Aquatic  and 
the  Terrestrial  Carnivora. 

The  terrestrial  Carnivora  were  formerly  classed  as  “digitigrade  ” 
and  “  plantigrade,”  a  classification  exceedingly  inconvenient,  as  it 
left  the  greater  number  of  the  animals  to  be  classified  in  the  de- 
bateable  ground  between  the  two  extreme  types.  As  a  linear 
classification  is  impossible,  they  are  now  grouped  around  three 
centres :  the  CEluroidea,  or  cat-like ;  the  Cynoidea,  or  dog-like ; 
and  the  Arctoidea,  or  bear-like  Carnivora  ;  and,  instead  of  taking 
the  FelidaB,  or  Cats,  as  the  type  of  the  group,  it  is  generally  con¬ 
sidered  that  the  Dog  tribe  are  the  most  generalised  form,  and  that 
the  Cats  are  an  extreme  modification  in  one  direction,  the  Bears  in 
another. 

The  Cynoidea  comprise  the  Dog,  and  its  immediate  allies,  the 
Wolves  and  Foxes. 

The  CEluroidea,  or  Cat-like  Carnivora,  comprise  the  Yiverridee 
(Civets),  Hyaenas,  and  Cats. 

The  Arctoidea,  or  Bear-like  Carnivora,  comprise  the  Mustelidae 
(Weasels),  Procyonidae  (Racoons),  and  the  true  Bears. 

The  order  Carnivora  is  a  very  natural  one,  and  its  name  is,  upon 
the  whole,  fairly  descriptive  of  the  habits  of  the  majority  of  its 
members  ;  though  there  are  some  creatures  included  in  it  which  are 
mixed  feeders,  and  others  which  are  purely  vegetarian. 

In  carnivorous  animals  one  tooth  on  each  side  of  both 
upper  and  lower  jaws  is  of  considerable  length,  is  sharply 
pointed,  and  is  called  a  canine ;  the  upper  canine  is  sepa¬ 
rated  by  an  interval  from  the  incisors,  the  lower  canine 


422 


A  MANUAL  OF  DENTAL  ANATOMY. 


being  received  into  the  vacant  space  or  “diastema”  so 
formed. 

The  incisors  are  short,  almost  always  six  in  number,  and 
stand  nearly  in  a  straight  line,  transversely  across  the  front 
of  the  jaw,  the  outermost  upper  incisor  being  sometimes 
large  and  pointed  so  as  to.  be  like  a  small  canine. 

The  incisors  and  canines  may,  on  the  whole,  be  said  to  be 
tolerably  uniform  throughout  the  order,  but  the  variations 
in  the  premolar  and  molar  teeth  are  both  numerous  and 
interesting. 

In  the  most  purely  carnivorous  members  of  the  order, 


Fig.  181  l1). 


the  Felidae,  the  true  molars  are  reduced  to  a  minimum,  and 
the  back  teeth  are  thin  edged,  “  sectorial  ”  teeth ;  in  the 
bears,  on  the  other  hand,  some  of  which  are  purely  her¬ 
bivorous,  the  molars  are  little  short  of  the  full  typical  mam¬ 
malian  number,  and  are  furnished  with  obtuse  and  broad 
grinding  surfaces. 

The  accompanying  figure  will  serve  to  give  the  general 
aspect  of  the  teeth  and  jaws  of  a  typically  carnivorous 
animal,  and  to  show  the  great  development  of  the  processes 

(b  Side  view  of  the  cranium  of  a  Tiger,  with  the  mouth  slightly  opened 
to  show  the  relative  position  of  the' great  canines. 


THE  TEETH  OF  CARNIVORA. 


123 


for  the  attachment  of  muscles,  and  the  stout  wide  arch  of 
the  zygoma. 

To  a  particular  tooth  in  the  upper  jaw,  and  to  its  antago¬ 
nist  in  the  lower  jaw,  Cuvier  gave  the  name  of  “  carnassial 
these,  conspicuous  in  the  true  flesh-feeders,  become  less  dif¬ 
ferentiated  in  the  Arctoidea  or  bear-like  Carnivora,  and  in 
the  bears  themselves  are  indistinguishable  from  the  other 
teeth,  save  by  a  determination  of  their  homologies  by  a 
process  of  comparison  with  the  teeth  of  intermediate 
forms. 

The  sectorial  or  carnassial  tooth  in  the  upper  jaw  is 
always  the  fourth  premolar  ;  its  crown  is  divisible  into  two 
parts,  the  one  a  thin  sharp-edged  blade,  which  runs  in  an 
antero-posterior  direction,  and  is  more  or  less  divided  by  one 
or  two  notches  into  a  corresponding  number  of  cusps  ;  the 
other  part,  the  “  tubercle,”  is  a  shorter  and  blunter  cusp, 
and  supported  upon  a  distinct  inner  root  situated  at  the 
inner  side  of  the  anterior  end  of  the  blade  (see  fig.  182). 
In  those  which  are  most  purely  flesh-feeders,  the  “blade”  is 
wTell  developed,  and  the  tubercle  of  small  size  ;  an  increase 
in  the  tubercular  character  of  the  tooth  is  traceable  through 
those  genera  which  are  mixed  feeders. 

Thus  in  the  bears  the  tubercle  is  said  to  be  highly 
developed,  but  it  is  to  be  noted  that  the  large  flattened 
inner  portion  of  the  bear’s  sectorial  tooth  is  in  a  more 
posterior  position  than  the  tubercle  of  a  cat’s  sectorial,  and 
is  not  supported  upon  any  separate  root. 

The  lower  tooth  which  antagonises  the  upper  carnassial, 
passing  a  little  behind  it,  is  the  first  true  molar  ;  in  the 
Felidrn  it  consists  solely  of  the  blade,  which  is  divided  into 
two  large  cusps,  behind  which  is  a  very  small  and  rudimen¬ 
tary  third  division  (which  in  the  Hysenidse,  for  example,  is 
of  conspicuous  dimensions).  In  existing  Carnivora  but  one 
“  sectorial  ”  tooth  is  to  be  found  on  each  side  of  the  jaws,  but 
in  the  Hysenodon,  which  had  the  full  number  of  44  teeth, 


424 


A  MANUAL  OF  DENTAL  ANATOMY. 


and  in  some  other  extinct  tertiary  mammals  there  were  more 
teeth  partaking  of  this  character. 

In  a  general  sense  we  may  say  that  the  characters  which 
indicate  a  pure  flesh  diet  are  :  the  small  size  of  the  incisors 
as  compared  with  the  canines,  and  their  arrangement  in  a 
straight  line  across  the  jaw ;  the  large  size,  deep  implanta¬ 
tion,  and  wide  separation  from  one  another  of  the  canines ; 
the  reduction  in  number  of  the  molar  series,  those  that 
remain  being  without  broad  crushing  surfaces,  in  the  place 
of  which  a  pointed  or  sharp-edged  form  prevails. 

Thus  the  more  numerous  the  teeth  of  the  molar  series, 
and  the  broader  their  crowns,  the  more  likely  it  is  that  the 
creature  subsists  upon  a  mixed  diet ;  and  a  gradation  may 
be  traced  even  in  individual  teeth,  such  as  the  carnassials, 
in  which  a  gradual  increase  in  relative  size  of  the  internal 
tubercular  cusps  of  the  upper,  and  of  the  posterior  tubercles 
of  the  lower  teeth,  may  be  traced  as  we  pass  from  the  ex¬ 
amination  of  the  teeth  of  Felidae,  to  those  of  mixed  feeders, 
such  as  the  Arctoidea. 

It  is  a  familiar  observation  that  immature  animals  differ 
less  from  their  allies  than  do  the  respective  adults,  and  this 
is  exemplified  by  the  milk  dentition  of  the  present  order. 

With  the  exception  of  the  Felidae,  which  have  only  two 
lower  milk  molars,  the  terrestrial  Carnivora,  so  far  as  is 
known,  all  have  the  same  milk  dentition  : 

.31  3 

i  -  c  -  m  -  . 

3  1  3 

Cy noidea . — The  dog  presents  almost  the  full  typical 
number  of  teeth,  one  upper  molar  (present  in  an  extinct 
dog-like  animal,  the  Amphicyon)  alone  being  wanting. 

.31  42 

i  —  c  —  pm  -  m  - . 

3  1  1  4  3 

The  incisors  are  small,  the  outermost  being  the  largest ; 
the  upper  incisors  have,  as  in  a  great  many  Carnivora,  a 


THE  TEETH  OF  CARNIVORA 


425 


tri-lobed  shape,  the  surface  of  the  crown  being  marked  by  a 
transverse  groove  into  which  the  apex  of  the  lower  tooth 
fits,  and  the  anterior  of  the  lobes  thus  formed  being  notched 
so  as  to  divide  it  into  two. 


Fig.  182  (l). 


The  canines,  large  and  conical,  are  somewhat  compressed 
from  side  to  side,  and  have  an  anterior  and  a  posterior  sharp 
ridge  ;  they  are  also  slightly  flattened  on  their  inner  surface. 

The  premolars  are  flattened  from  side  to  side,  pointed, 
increasing  in  size  from  before  backwards,  and  have  small 

1 1 

(!)  Dentition  of  Australian  Dog  (Canis  Dingo). 

(2)  Milk  and  permanent  teeth  of  Dog  (after  Prof.  Flower). 


426 


A  MANUAL  OF  DENTAL  ANATOMY. 


basal  accessoiy  cusps  (see  fig.  182).  The  fourth  upper  pre¬ 
molar  is  the  sectorial  tooth,  and  is  very  much  larger  than 
the  third  premolar ;  the  blade  is  well  pronounced,  and  the 
tubercle  small.  The  fourth  lower  premolar  does  not 
greatly  differ  from  the  third.  The  two  upper  true  molars 
are  blunt,  broad-crowned  tuberculated  teeth,  but  the  second 
is  very  small. 

In  the  lower  jaw  the  first  true  molar  or  carnassial  tooth 
has  a  well-marked  blade,  which  articulates  with  the  blade 
of  the  upper  carnassial  tooth ;  but  towards  the  posterior 
border  there  is  a  somewhat  thick  and  blunt  tuberculate 
portion,  barely  represented  in  the  corresponding  tooth  of 
the  Felidae;  the  tubercular  portion  articulates  with  the 
broad  flat  first  upper  molar.  The  second  lower  molar  is 
smaller,  not  being  one-fourth  the  size  of  the  first ;  the  third 
smaller  still ;  both  are  blunt-crowned  tuberculated  teeth 
(the  third  lower  molar,  rudimentary  in  all  dogs,  is  alto¬ 
gether  absent  in  the  Canis  primsevus).  The  fox-like 

4 

Otocyon,  however,  has  m  -,  making  up  a  total  of  48  teeth, 

4 

an  excess  over  the  full  mammalian  dentition. 

The  dentition  of  the  dog,  closely  similar  as  it  is  to  that 
of  the  wolves  and  foxes,  is  such  as  to  allow  of  a  considerable 
range  of  diet,  there  being  tubercular  molar  teeth  in  addition 
to  a  full  armament  of  such  sharply-pointed  teeth  as  are 
characteristic  of  flesh-feeding  animals. 

Thus  the  Canidae,  uniform  as  they  are  in  dentition,  have 
somewhat  different  habits ;  the  Arctic  fox,  a  flesli-feeder 
purely,  has  a  dentition  indistinguishable  from  the  North 
Italian  fox,  which  is  reputed  to  be  vegetarian  in  its  diet ; 
the  Canis  cancrivorus  of  Guiana,  which  often  possesses  a 
fourth  molar,  eats  small  mammals,  crabs,  and  also  fruit. 
Hence  it  is  necessary  to  be  very  careful  in  deducing  from 
the  character  of  the  teeth  what  may  probably  have  been 
the  diet  of  the  animal ;  an  approximate  idea  may  often  be 


THE  TEETH  OF  CARNIVORA. 


427 


reached,  but  the  sources  of  fallacy  are  sufficiently  numerous 
to  render  the  conclusion  uncertain. 

Amongst  the  various  breeds  of  dogs  some  slight  differ¬ 
ences  exist.  Thus  in  the  long-muzzled  races  considerable 
intervals  exist  between  the  premolars,  as  is  to  some  extent 
seen  in  C.  Dingo  (fig.  182),  while  in  the  short-muzzled  races 
the  teeth  are  in  contact,  and  set  somewhat  obliquely,  so  as 
to  be  almost  imbricated. 

On  the  whole  it  may  be  said  that  the  teeth  are  less  easily 
susceptible  of  modification  in  size  than  are  the  jaws,  so  that 
crowding  of  the  teeth  is  induced  by  selective  breeding  aiming 
at  the  production  of  short-muzzled  varieties. 

In  some  long-muzzled  races  supernumerary  teeth  are 
sometimes  found ;  thus  De  Blainville  (Osteographie, 
Caniclce)  figures  two  examples,  the  supernumerary  tooth 
being  in  one  case  a  premolar,  in  the  other  a  true  molar. 


(Eluroidea. — With  a  dental  formula  not  differing  much 
from  the  dog  (and  not  at  all  from  Canis  primaevus)  the 
Yiverridse  (Civet  cats,  Ichneumons,  &c'.),  approach  the  more 
typical  carnivores  in  such  points  as  the  thinner  and  sharper 
blades  of  the  premolar  teeth  and  the  greater  relative  length 
and  sharpness  of  the  canines. 

The  dental  formula  is 


4 

_  m 
4 


2 

9* 


At  the  same  time  the  lower  carnassial  tooth  has  no  less 
than  six  sharply  pointed  cusps,  and  it  lacks  the  typical 
character  of  a  sectorial  tooth,  while  the  long  pointed  cusps 
of  the  molars  of  some  Viverridse  recall  the  characters  of 
insectivorous  dentitions  rather  than  those  of  true  flesh- 
feeders  ;  furthermore,  there  are  other  Viverridee  which  are 
not  at  all  savage,  and  which  subsist  on  a  diet  of  fruits, 
eggs,  &c. ,  such  as  the  Binturong  or  the  Paradoxurus,  the 


428 


A  MANUAL  OF  DENTAL  ANATOMY. 


teeth  of  which  have  almost  lost  the  carnivorous  character. 
Little  use  can  therefore  be  made  of  the  Viverrida3  as  illus¬ 
trating  the  transition  between  the  dental  characters  of  the 
other  families  of  the  order  ;  they  rather  serve  to  exemplify 
how,  within  the  limits  of  a  single  family,  with  an  identical 
dental  formula,  the  form  and  size  of  the  teeth  may  vary  so 
as  to  adapt  its  members  to  different  forms  of  food  and  habits 
of  life. 

HycmidcE. — In  the  Hyaena  the  jaw  is  short  and  stout;  the 


Fig.  184  (J). 


canines  are  set  far  apart,  and  the  teeth  of  the  molar  series 
are  reduced  in  number. 


The  incisors  are  short  and  stout,  but  the  outermost 
upper  incisor  is  somewhat  caniniform ;  the  canines  are  very 

(r)  Upper  ancl  lower  teeth  of  Hysena.  The  strongly  marked  cingulum 
is  seen  upon  the  lower  teeth.  In  the  upper  jaw  the  fourth  premolar 
(carnassial  tooth)  has  a  strong  blade,  divided  into  three  cusps,  and  a 
small  tubercle  opposite  to  and  within  the  anterior  cusp  ;  it  is  a  good 
typical  carnassial  tooth. 


429 


THE  TEETH  OF  CARNIVORA. 


strong,  but  are  not  so  long  relatively  to  the  other  teeth  as 
in  the  Feliche. 

The  premolars  are  all  stout  pointed  teeth,  with  a  very 
well  pronounced  basal  ridge  or  cingulum,  serviceable  in 
protecting  the  gums  when  the  creature  is  crushing  up  bones ; 
they  increase  in  size  from  before  backwards  in  the  upper 
jaw,  the  fourth  upper  premolar  being  a  well-marked  carnassial 
tooth  with  its  blade  and  tubercle. 

The  lower  carnassial  or  first  molar  consists  of  little  more 
than  the  notched  blade ;  but  the  little  posterior  tubercle  so 
strongly  pronounced  in  the  dog,  is  in  the  hyaena  distinctly 
more  marked  than  in  the  Felidae  (cf.  figs.  184  and  185). 
The  only  upper  true  molar  is  the  rudimentary  tooth,  placed 
inside  the  back  of  the  fourth  premolar. 

The  main  feature  of  the  dentition  of  the  hyaena  is  the 
great  stoutness  and  strength  of  the  teeth ;  they  are  admir¬ 
ably  adapted  to  the  habits  of  the  animal,  which  feeds  rather 
upon  the  portions  of  Carcasses  left  by  the  fiercer  carnivora 
than  upon  those  which  it  kills  for  itself,  and  consequently 
bones  form  a  large  proportion  of  its  food. 

There  is  a  curious  hyaena-like  animal  found  at  the  Cape 
(of  which  there  are  often  specimens  at  the  Zoological 
Gardens)  called  Proteles  or  Aardwolf,  in  which  the  teeth 
of  the  molar  series  are  quite  rudimentary.  The  incisors 
(much  worn  in  old  animals)  and  the  canines  are  fairly  well 
developed ;  the  molars  and  premolars  quite  stunted. 


The  deciduous  dentition 


is  similar  to  the 


adult,  as  respects  the  teeth  being  stunted.  It  is  a  cowardly 
animal,  and  is  supposed  to  feed  on  putrid  flesh  ;  it  is  said  to 
eat  young  lambs,  and  to  bite  the  large  tails  of  the  Cape 
sheep,  which  are  remarkable  for  containing  an  abundance  of 
semi-fluid  fat. 


430 


A  MANUAL  OF  DENTAL  ANATOMY. 


Felidce. — The  dentition  of  this  family  is  singularly 
uniform. 

.313  1 

i  -  c  -  p  —  m  _ . 

3  1  1  2  1 

Thus  the  molar  series  is  reduced  below  that  of  hyaena  by 
the  loss  of  a  premolar  in  both  jaws.  The  incisors  are  very 
short,  the  canines  very  large,  widely  cipart,  and  sharply 
pointed,  with  a  pronounced  longitudinal  ridge  very  charac¬ 
teristic  of  the  Felidae  ;  the  premolars  nearest  to  them  are 


Fig.  185  (’>. 


quite  short,  so  that  they  stand  practically  alone,  and  so  can 
penetrate  the  flesh  of  living  prey  more  readily. 

The  first  upper  (really  the  second  of  the  typical  mam¬ 
malian  dentition)  premolar  is  almost  a  rudimentary  tooth ; 
the  second,  a  far  larger  tooth,  is  sharply  pointed ;  the  third  is 
a  well  pronounced  carnassial  tooth,  of  which  the  “  blade  ”  is 
divided  by  two  notches  into  three  sharp  lobes,  with  the  middle 
one  of  which  the  “tubercle”  is  connected  by  a  slight  ridge. 

The  solitary  true  molar  is  a  small  tooth,  placed  trans- 


f1)  Side  view  of  lower,  and  palatal  aspect  of  upper  jaw  (Leopard). 


♦ 


THE  TEETH  OF  CARNIVORA. 


431 


versely,  and  within  the  back  of  the  premolar,  so  that  looking 
from  the  outside  it  is  not  visible  at  all. 

In  the  lower  jaw  the  carnassial  (first  molar)  is  reduced  to 
the  “  blade  ”  only  ;  it  is  divided  by  a  Y-shaped  notch  into 
two  lobes,  and  the  posterior  tubercle  is  hardly  represented. 

In  an  extinct  feline  animal,  the  Machairodus,  found  in 
tertiary  strata,  and  very  widely  distributed  (in  France, 
Italy,  India,  Brazil,  Buenos  Ayres)  the  first  of  the  pre- 
molars  left  in  the  upper  jaw  of  Felis,  and  there  almost 
rudimentary  (see  fig.  185),  has  disappeared;  the  dental 
formula  is  thus  : 


The  upper  canines  are  of  immense  length,  and  the  ridge 
of  enamel  which  runs  down  the  front  and  back  surface  of 


Fig.  186  f1). 


the  teeth  is  distinctly  serrated ;  hence  the  name  of  saw- 
toothed  Tiger  which  has  been  given  to  the  animal. 

,  The  lower  canines  are  quite  small,  and  ranged  with  the  ' 

f1)  Side  view  of  the  jaws  and  cranium  of  Machairodus  (Drepanodon), 
after  Owen. 


432 


A  MANUAL  OF  DENTAL  ANATOMY. 


incisors.  The  enormous  length  of  the  upper  canine  renders 
it  difficult  to  see  in  what  manner  it  was  made  use  of,  as  the 
mouth  could  hardly  have  been  opened  to  an  extent  sufficient 
to  enable  its  point  to  do  more  than  clear  the  lower  jaw. 

Smilodon,  a  somewhat  similar  extinct  animal,  had  a  den¬ 
tition  still  further  reduced,  viz.  : 


3  1  2 

—  c  —  p  - 

2  1  1  2  or  1 


0 

r 


m 


Prof.  Cope  has  described  a  rich  series  of  extinct  cats 
(“  Extinct  Cats  of  N.  America,”  American  Naturalist,  Dec. 
1880),  mostly  from  Miocene  beds.  He  summarises  their 
characters  thus  : 

“It  is  readily  perceived  that  the  genera  above  enumerated 
form  an  unusually  simple  series,  representing  stages  in  the 
following  modification  of  parts  :  — 

(1.)  In  the  reduced  number  of  molar  teeth. 

(2.)  In  the  enlarged  size  of  the  upper  canine  teeth. 

(3.)  In  the  diminished  size  of  inferior  canine  teeth. 

(4.)  In  the  conic  form  of  the  incisors. 

(5.)  In  the  addition  of  a  cutting  lobe  to  the  anterior 
base  of  the  upper  sectorial  tooth. 

(6.)  In  the  obliteration  of  the  inner  tubercle  of  the  lower 
sectorial. 

(7.)  In  the  extinction  of  the  heel  of  the  same. 

(8.)  In  the  development  of  an  inferior  flange  at  the 
latero-anterior  angle  of  the  front  of  the  ramus  of 
the  lower  jaw. 

(9.)  In  the  development  of  cutting  lobes  upon  the 
posterior  border  of  the  large  premolar  teeth. 

The  succession  of  the  genera  above  pointed  out,  coincides 
with  the  order  of  geologic  time  very  nearly. 

The  relations  of  these  genera  are  very  close,  as  they  differ 
in  many  cases  by  the  addition  or  subtraction  of  a  single  tooth 
from  each  dental  series. 


THE  TEETH  OF  CARNIVORA. 


433 


These  characters  are  not  even  always  constant  in  the  same 
species,  so  that  the  evidence  of  descent,  so  far  as  the 
genera  are  concerned,  is  conclusive.  No  fuller  genealogical 
series  exists  than  that  which  I  have  discovered  amongst  the 
extinct  cats.” 

The  extinct  Hytenodon  in  some  respects  resembled  the 
Felidae,  though  it  is  on  the  whole  of  somewhat  doubtful 
affinities  :  it  differed  in  that  it  presented  the  typical  mam¬ 
malian  formula  of 


3 

3 


i 


its  great  peculiarity  being  that  one  and  all  of  these  teeth 
were  of  “  carnassial  ”  (J)  form.  Yet  the  elongated  form  of  its 
jaw  is,  so  far  as  it  goes,  opposed  to  the  idea  of  its  having 
been  highly  carnivorous ;  its  food  at  all  events  must  probably 
have  consisted  of  animals  very  much  smaller  than  itself. 

Arctoidea. — Amongst  the  Carnivora  grouped  together  by 
many  characteristics  as  ‘  bear-like,’  a  tolerably  complete  gra¬ 
dation  of  character  in  the  matter  of  dentition  may  be  traced. 

Some  of  the  group,  such  as  the  stoats  and  martins,  are 
very  carnivorous  ;  others  are  mainly  herbivorous.  Of  the 
Mustelidse  the  dental  formula  is 


3  14  1 

_  c  —  p  -  m  - 

O  1  -L  A  Cl 


There  is  a  sort  of  primd  facie  resemblance  to  the  feline 
dentition,  for  the  sectorials  are  very  much  like  those  of  the 
Felidae,  but  the  last  tooth  in  each  jaw  is  a  broad  topped 
tubercular  molar,  even  in  the  most  carnivorous  members  of 
the  group,  while  in  those  which  are  less  so,  such  as  the 
badger,  the  molar  teeth  are  very  broad  and  obtuse,  the 

[})  Tlie  carnassial  tooth  of  Felidse  is  always  opposite  to  the  corner  of  the 
lips  :  if  further  forward  it  would  act  at  a  disadvantageous  leverage,  and 
if  further  back,  could  not  be  got  at  for  slicing  pieces  off'  a  carcase  too  large 
to  take  bodily  into  the  mouth  (Cope.) 


F  F 


434 


A  MANUAL  OF  DENTAL  ANATOMY. 


lower  sectorial  having  a  very  small  blade  and  a  very  large 
tubercular  posterior  talon,  so  that,  without  having  really 
lost  its  typical  formation  it  comes  practically  to  be  a  broad 
grinding  tooth. 

In  the  Procyonidse  (Racoons  and  Coatimundis,  &c.),  we 
have  a  further  departure  from  the  carnivorous  character, 
in  the  increased  development  of  the  molar  series:  the  dental 
formula  is 


In  the  Coatimundi,  for  example,  the  upper  sectorial 


Fig.  187  fl). 


has  a  very  large  “  tubercle,”  and  posteriorly  to  this  there 
is  a  small  additional  tubercle  ;  the  “blade  ”  has  no  large  or 
conspicuous  thin,  flat,  sharp  edge,  but  presents  two  pro¬ 
nounced  cusps. 

The  lower  sectorial  is  no  longer  recognisable  as  a  car- 
nassial  tooth,  and  all  the  true  molars  are  broad  teeth  with 
four  or  five  cusps. 

(l)  Upper  and  lower  teeth  of  a  Coatimundi  (Nasua  socialis).  The  fourth 
upper  premolar  (carnassial  tooth)  has  lost  its  sectorial  character  by  the 
blade  being  much  less,  and  the  tubercle  much  more,  developed  than  in  the 
(Eluroidea  ;  there  is  an  additional  internal  tubercle  at  the  back  of  the 
tooth. 


THE  TEETH  OF  CARNIVORA. 


435 


The  canines  are  very  peculiar,  those  of  the  upper  jaw 
being  very  straight  and  much  flattened  from  side  to  side  ; 
those  of  the  lower  jaw  strongly  curved,  and  marked  by  a 
deep  groove  near  the  front  of  their  anterior  surface. 

In  the  Bears  the  teeth  are  yet  further  modified  to  suit 
the  requirements  of  mixed  or  vegetable  feeders. 

The  dental  formula  is  generally — • 


The  incisors  of  the  upper  jaw  present  the  notch  across 
the  crown,  so  common  in  Carnivora,  and  the  outermost  is 

Fig.  188  {'). 


large  and  not  unlike  a  canine ;  the  canines  are,  relatively 
to  the  other  teeth,  not  so  large  as  in  dogs  or  Felidte  ;  never¬ 
theless  they  are  stout  strong  teeth,  upon  which  the  anterior 
and  posterior  ridges  of  enamel  are  well  marked. 

The  first  three  premolars  are  small  dwarfed  teeth  ;  the 
first  premolar  is  very  close  to  the  canine,  and  has  a  crown 
of  peculiar  form,  produced  out  towards  the  canine. 

fl)  Teetli  of  a  ’Bear  (Ursus  thibetanus  ?).  The  figure  is  drawn  from  a 
young  specimen,  in  which  the  canines  have  hardly  attained  to  their  full 
length.  In  this  bear  the  four  premolars  are  all  persistent. 


F  F  2 


436 


A  MANUAL  OF  DENTAL  ANATOMY. 


All  four  of  the  premolars  seldom  persist  through  the  life¬ 
time  of  the  animal ;  the  first  premolar,  however,  is  rarely 
(if  ever  in  recent  species)  lost,  the  second  being  the  first  to 
fall  out,  and  then  the  third.  As  the  fourth  is  never  lost,  in 
most  adult  bears  the  first  and  fourth  premolars  are  found, 
with  a  wide  interval  between  them.  The  premolars  of  bears 
thus  form  an  exception  to  the  rule  that  when  a  tooth  is  lost 
from  the  premolars,  the  loss  takes  place  from  the  front  of 
the  series. 

The  fourth  upper  premolar  (carnassial  tooth)  retains 
something  of  its  carnassial  character,  though  relatively  to 
other  teeth  it  is  smaller  than  in  the  Felidie  ;  the  first  lower 
molar  very  little,  save  that  it  is  a  narrower  and  more 
elongated  tooth  than  the  other  true  molars. 

The  other  true  molars  are  squarish  or  oblong  teeth,  raised 
into  blunt  tubercular  cusps  ;  they  vary  in  different  species. 

In  the  sloth  bear  (Melursus  labiatus)  the  incisors  are  small 
and  the  median  pair  are  lost  early ;  it  is  variously  stated 
to  be  frugivorous  and  to  feed  on  ants,  the  latter  probably 
being  the  more  truthful  account. 


Carnivora  Pinnipedia  (Seals). 

The  aquatic  Carnivora  are  divided  into  three  families  : — 

I.  The  Otariidse,  or  Eared  Seals,  comprising-  the  sing-le  genus  Otaria, 

known  as  Sea  Lions,  or  Sea  Bears.  These  are  the  “  fur  Seals.” 
from  which  seal  skin  is  procured,  and  they  are  less  removed 
from  the  terrestrial  carnivora  than  are  the  other  seals  :  the 
limbs  are  better  adapted  for  walking-,  there  are  external 
ears,  &c. 

II.  The  Phocidse,  to  which  family  the  seals  of  our  own  coasts 

(Phoca  greenlandica,  &c.)  and  the  Great  Proboscis  Seals  of  the 
southern  seas  (Cystophora)  belong. 

III.  The  Trichechidae,  or  Walruses,  an  aberrant  Arctic  family  con¬ 
sisting  of  one  genus  only. 

The  dentition  of  the  seals  is  less  highly  specialised  than 


THE  TEETH  OF  CARNIVORA 


437 


that  of  other  Carnivora,  in  some  cases  approximating  to  that 
of  homodont  Cetaceans. 

The  seals  belong  to  the  less  powerfully  developed  orders  of 


Fig.  189  (’). 


mammalia,  and  like  others  similar  in  this  respect,  have  no 
change  of  functional  teeth. 

What  change  there  is  takes  place  at  an  exceedingly  early 
period,  indeed  at  or  before  birth. 

(!)  Jaws  of  Otaria,  in  which  the  teeth  are  affected  by  a  form  of  erosion. 
After  Dr.  Murie.  Odont.  Soc.  Trans.,  1870. 


438 


A  MANUAL  OF  DENTAL  ANATOMY. 


The  milk  dentition  is  very  feebly  developed  in  all  seals ; 
in  the  Otaria  (fur  seal)  which  of  all  the  seals  most  approaches 
to  the  terrestrial  carnivora  in  other  characters,  the  milk  teeth 
are  retained  for  a  few  weeks,  but  in  most  others  they  are 
shed  about  the  time  of  birth.  Thus  Professor  Flower 
tells  us  that  in  a  Phoca  greenlandica  a  week  old  scarcely  a 
trace  of  the  milk  teeth  was  left. 

The  canines  are  generally  well  marked  by  being  larger 
than  the  other  teeth,  but  the  molars  and  premolars  are 
very  similar  to  each  other,  and  are  simple  in  pattern. 

The  teeth  of  Otaria  and  of  some  other  seals  become 


Fig.  190  p). 


much  worn  down,  and  they  also  seem  to  become  eroded  at 
the  level  of  the  gums,  as  they  are  often  deeply  excavated  at 
points  which  seem  unlikely  to  have  been  exposed  to  friction, 
but  the  nature  of  this  erosion  has  not  been  adequately  in¬ 
vestigated. 

The  incisors,  however,  vary  in  number  in  different  groups, 
while  the  canines,  premolars,  and  molars  are  constant. 

The  common  seals  (Phoca)  have  a  dental  formula 


The  incisors  are  of  simple  form,  and  the  outer  are  the 
larger.  The  canine  is  a  strong  recurved  tooth,  with  a 
large  root ;  behind  it  follows  a  series  of  molars,  each  of 


P)  Teeth  of  Phoca  greenlandica. 


THE  TEETH  OF  CARNIVORA. 


439 


i 


I 


which  (with  the  exception  of  the  first)  bears  a  central 
principal  cusp,  with  a  smaller  accessory  cusp  before  and 
behind  it.  The  forms  of  the  crowns  vary  a  good  deal  in 
different  genera,  in  some  the  cusps  being  much  larger, 
more  deeply  separated  from  one  another  and  recurved ;  and 
in  others  the  accessory  cusps  being  multiplied,  so  that  the 
name  of  “  saw-toothed  seal  ”  has  been  given  to  their  pos¬ 
sessor. 

It  is  suggested  by  Baume  that  the  degree  to  which  the 
teeth  have  become  simplified  perhaps  corresponds  with  the 
antiquity  of  the  genus  as  aquatic,  those  which  have  taken 
to  the  wTater  more  recently  having  retained  a  greater 
complexity  of  tooth  crown. 

The  Leopard  Seal  has  teeth  with  exceedingly  long  roots, 
disproportionate,  one  would  say,  to  its  necessities  for  firm 
implantation  of  its  teeth. 

In  the  Hooded  seals  (Cystophora)  the  incisors  are  reduced 


Fig.  191  (l). 


to  one  in  the  lower  jaw  and  two  in  the  upper ;  the  canines 
are  of  great  size,  but  the  molars  are  small  and  simple 
in  form,  so  as  to  approximate  to  the  teeth  of  the  Cetacea. 

(l)  Permanent  and  milk  teeth  of  Elephant  Seal  (Cystophora  proboscidea). 


440 


A  MANUAL  OF  DENTAL  ANATOMY. 


The  walrus  (Trichechus  rosmarus),  an  aberrant  Arctic 
form,  is  possessed  of  enormous  upper  canines,  which  pass 
down  outside  the  lower  lip,  and  are  of  such  dimensions  as 
to  materially  modify  the  form  of  cranium  by  the  size  of 
their  sockets  ;  they  grow  from  persistent  pulps,  and  are 
composed  of  dentine  with  a  thin  investment  of  cement. 


Fig.  192  (J). 


The  great  tusks  are  employed  to  tear  up  marine  plants 
and  to  turn  over  obstacles,  the  walrus  feeding  upon  Crus¬ 
tacea,  and  also  upon  seaweed,  &c. ;  they  are  also  used  to 

d)  Side  view  of  upper  and  lower  jaws  of  a  Walrus  (Trichechus  rosmarus). 
The  upper  jaw  has  been  tilted  a  little  to  one  side,  in  order  to  bring  into 
view  the  molar  teeth  at  the  same  time  with  the  long  tusks.  The  deter¬ 
mination  of  the  teeth  being  open  to  question,  they  have  been  simply 
numbered. 


THE  TEETH  OF  CARNIVORA. 


441 


assist  the  animal  in  clambering  over  ice  :  as  they  are  of 
almost  equal  size  in  the  female,  they  cannot  be  regarded  as 
weapons  of  sexual  offence,  but  they  are  undoubtedly  used 
in  the  combats  of  the  males. 

The  largest  tusks  seen  by  Nordenskiold  were  30  inches  in 
length,  and  8  inches  in  circumference  ;  the  tusks  of  the 
females  attain  to  the  same  length,  but  they  are  much  more 
slender. 

In  addition  to  the  great  tusks  the  walrus  ordinarily  has  a 
row  of  four  or  five  teeth,  short  and  simple  and  worn  down  to 
the  level  of  the  gums.  Of  these,  the  one  placed  immediately 
within  the  base  of  the  great  canine  is  in  the  intermaxillary 
bone,  and  is  hence  an  incisor  :  the  ordinary  dental  formula 
is  given  by  Professor  Flower  as 


But  there  is  some  difficulty  in  assigning  a  definite  dental 
formula :  for  in  front  of  the  solitary  incisor  are  often  the 
sockets  (or  even  the  teeth  themselves)  of  two  others,  which 
are  for  various  reasons  rather  to  be  regarded  as  non-per¬ 
sistent  teeth  of  the  permanent  set  than  as  milk  teeth ; 
and  there  are  also  small  teeth  sometimes  to  be  met  with 
behind  the  molars,  which  seem  to  be  rudimentary  perma¬ 
nent  teeth. 

In  young  specimens  the  dentition  is 


5 

4 


3  1  * 


The  teeth  above  alluded  to  may  persist  through  life,  and 
probably  often  do ;  but  they  are  sure  to  be  lost  in  macerated 
skulls,  as  they  have  but  little  socket.  Of  the  milk  den¬ 
tition  four  teeth  have  been  traced  in  each  jaw;  they  are 
rudimentary,  are  lost  about  the  time  of  birth,  and  corre¬ 
spond  in  position  to  the  more  largely  developed  teeth  of  the 


442 


A  MANUAL  OF  DENTAL  ANATOMY. 


adult.  Hence  the  question  if  those  small  rudimentary- 
teeth  above  alluded  to  are  to  be  regarded  also  as  milk 
teeth  which  are  long  retained,  or  as  rudimentary  permanent 
teeth ;  at  present  this  requires  further  elucidation. 


The  Teeth  of  Primates.  * 

The  order  Primates  embraces  Man,  Monkeys,  and  the 
Lemurs.  * 

Some  naturalists  have  been  disposed  to  separate  the  Lemuridas 
from  the  rest  of  the  Primates,  on  the  ground  that  some  Lemurs 
approximate  rather  closely  to  the  Insectivora,  while  again  the  order 
Insectivora  contains  some  forms  which  recall  the  Lemurs. 

Prof.  Cope  regards  the  Lemurs  as  an  exceedingly  ancient  and 
generalised  form,  and  considers  that  they  may  have  been  parent 
forms  of  many  widely  different  mammalian  forms. 

But  although  the  Lemuridae  are  undoubtedly  inferior  to  the 
Monkeys,  and  stand  apart  from  them  more  widely  than  do  the 
Monkeys  from  Man,  most  authors  now  place  them  in  the  order 
Primates,  which  is  to  be  divided  as  follows  : — 

( Lemuridee.  Lemurs. 

Primates  <  Simiadae  Old  and  new  world  Monkeys. 

( Anthropidae.  Man. 

Lemuridae. — The  Lemurs  for  the  most  part  are  found  in 
Madagascar,  and  to  a  less  extent  on  the  mainland  of  Africa 
and  in  southern  Asia.  In  their  dentition,  just  as  in  other 
characters,  they  differ  somewhat  from  the  true  monkeys, 
though,  on  account  of  there  being  several  very  aberrant  in 
form,  it  is  difficult  to  give  any  general  account  of  them. 
Most  of  them  have  the  upper  incisors  very  small,  and  widely 
separated  from  one  another  ;  in  the  lower  jaw  these  are  antag¬ 
onised  by  six  or  eight  long,  thin,  narrow  procumbent  teeth, 
generally  regarded  as  being  two  pairs  of  incisors  and  the  lower 
canines :  in  both  upper  and  lower  jaws  the  next  tooth  is 


THE  TEETH  OF  PRIMATES . 


443 


large  and  pointed  like  a  canine,  but  the  lower  caniniform 
tooth  bites  behind  the  upper,  and  so  is  held  not  to  corre¬ 
spond  to  it,  but  to  be  the  first  premolar.  The  premolars 
are  compressed  from  side  to  side,  and  are  very  sharp  :  the 
molars  are  armed  with  long  sharp  cusps,  which  are  worn 
down  in  old  animals. 

The  upper  molars  in  many  lemurs  are  armed  with  four 
cusps,  connected  by  an  “  oblique  ridge  ”  like  those  of  man 
and  the  anthropoid  apes. 

In  many  of  them  the  lower  premolars  are  two  rooted,  the 
roots  being  more  or  less  completely  in  the  position  of  outer 
and  inner,  not  of  anterior  and  posterior  roots. 


Fig.  193  (]). 


There  is  a  very  aberrant  lemur,  the  Aye-aye  (Cheiromys), 
which  in  its  cfentition  imitates  the  rodents. 

.10  13 

i  —  c  —  pm  —  m  — 

1  0  1  0  3 

In  both  upper  and  lower  jaws  the  incisors  form  a  single 
pair  of  large  curved  teeth,  growing  from  persistent  pulps, 
and  wearing  obliquely  so  as  to  constantly  preserve  a  sharp 
cutting  edge.  The  enamel  is  very  much  less  thick,  if  not 
altogether  absent,  upon  the  backs  of  the  upper  incisors,  but 


0)  Teeth  of  the  Indri. 


444 


A  MANUAL  OF  DENTAL  ANATOMY. 


the  lower  incisor,  which  is  very  narrow  from  side  to  side, 
and  very  thick  from  back  to  front,  is  composed  very 
largely  of  enamel,  the  dentine  constituting  but  a  very  small 
part  of  it. 

After  a  considerable  interval,  which  is  devoid  of  teeth, 
there  [follow  four  upper  and  three  lower  teeth,  which  are 
not  of  persistent  growth,  but  have  definite  roots,  and  resemble 
the  molars  of  many  omnivorous  rodents. 

Being  a  somewhat  rare  and  strictly  nocturnal  animal, 
little  is  known  of  its  food ;  some  have  believed  that  it  makes 
use  of  its  rodent  incisors  to  cut  away  portions  of  wood  in 
order  to  get  at  the  grubs  contained  in  it,  drawing  them  out 
of  their  hiding  place  by  means  of  its  curiously  elongated 
finger,  whilst  others  believe  that  it  gnaws  the  sugar  cane. 
But  whatever  the  nature  of  its  food  may  be,  it  is  certain 
that  its  scalpriform  incisors  are  put  to  hard  wrork,  and  so 
kept  worn  down,  for  in  a  specimen  kept  for  a  time  in  the 
Zoological  Gardens,  which  was  supplied  with  soft  food, 
the  incisor  teeth  grew  to  an  excessive  length,  and  ultimately 
caused  the  animal’s  death  by  the  points  of  its  lower  incisors 
perforating  the  palate.  The  accompanying  figure  represents 
the  muzzle  of  this  specimen,  and  although  the  upper  teeth 
have  grown  to  an  inordinate  length,  and  have  diverged  from 
one  another,  it  will  serve  to  show  the  rodent-Jike  aspect  of 
its  mouth. 

Although,  functionally,  its  teeth  are  those  of  a  rodent, 
yet  despite  this  adaptive  resemblance,  the  milk  dentition 
retains  certain  characters  which  indicate  the  lemurine  origin 
of  the  creature. 

In  the  upper  jaw  the  milk  dentition  consists  of  two  small 
incisors,  a  canine  and  three  molars ;  in  the  lower  jaw  of  two 
small  incisors  and  two  small  molars ;  it  is  said  that  in  an 
early  stage  a  third  milk  incisor  is  to  be  found. 

The  permanent  incisors  push  their  way  up  between  the 
first  and  second  milk  incisors  :  at  a  certain  sta^re  all  three 


THE  TEETH  OF  PRIMATES. 


445 


are  to  be  seen  at  once,  but  the  large  size  of  the  permanent 
incisors  causes  the  speedy  loss  of  the  milk  incisors. 

No  known  rodent  has  so  many  milk  teeth,  nor  indeed  any 
milk  incisors  at  all ;  the  Aye-aye  thus  affords  an  excellent 
example  of  a  milk  dentition  preserving  characters  which  are 
lost  in  the  extremely  modified  adult  dentition. 

The  special  interest  which  attaches  to  the  dentition  of 


Fig.  194  (b. 


Cheiromys  has  been  'already  alluded  to ;  to  briefly  recapit¬ 
ulate,  it  is  this  :  in  Madagascar,  an  isolated  area  separated 
by  a  wide  tract  of  deep  sea  from  other  areas,  true  rodents 
are  almost  absent,  but  lemurs  abundant.  But  one  of 
the  lemurine  animals  which  are  to  be  found  there  has  been 
so  modified  that  its  teeth  to  all  intents  and  purposes 


(b  Aye-Aye  (Cheiromys),  which  died  in  the  Zoological  Gardens  (after 
Dr.  Murie).  The  upper  incisors,  from  want  of  sufficient  use,  have  grown 
long  and  diverged  from  the  middle  line. 


446 


A  MANUAL  OF  DENTAL  ANATOMY. 


are  those  of  a  rodent.  Yet  with  all  this  modification  it 
retains  characters  (notably  its  milk  dentition)  which  are 
quite  unlike  those  of  true  rodents,  but  which  recall  the 
manner  of  its  origin  from  higher  lemurine  forms. 

Fig.  195  0). 


Simiadae.  —  The  true  monkeys  are  divided  into  two 
great  divisions,  the  new  world  monkeys  and  the  old  world 
monkeys.  The  former  differ  in  many  respects  from  the 
latter ;  for  the  most  part  they  have  prehensive  tails,  and 
their  nostrils  are  set  somewhat  widely  apart,  whence  they 
are  called  Platyrrldne ,  or  wide-nosed  monkeys,  and  they 
differ  also  in  their  dental  formula,  which  is — 

(J)  Upper  and  lower  jaws  of  Cheirorays.  A.  Milk  dentition,  with  the 
permanent  incisors  just  emerging,  i,  l.  Upper  and  lower  permanent  in¬ 
cisors.  i  2,  12.  Upper  and  lower  milk  incisors,  c.  Milk  canines,  d  1, 
d  2,  d  a,  d  b.  Upper  and  lower  milk  molars.  (Twice  natural  size. )  B, 
Reduced  figure  of  permanent  teeth  (after  Peters). 


THE  TEETH  OF  PRIMATES. 


447 


.213  3  q/» 

i  —  c  —  p  —  m  —  =  36. 
2  1  1  3  3 


The  little  marmoset  monkeys  have  only  32  teeth,  but  they 
agree  with  the  other  new  world  monkeys  in  having  three 
premolars  on  each  side,  the  molars  being  reduced  to  two  in 
number.  The  upper  molars  of  some  new  world  monkeys, 
notably  Ateles  and  Mycetes,  have  the  antero-internal  and 
extero-posterior  cusps  joined  by  an  oblique  ridge,  a  character 
which  is  shared  in  the  old  world  groups  by  man  and  the 
anthropoid  apes  only. 

In  the  spider  monkeys  (Ateles)  the  outer  lower  incisors  are 
caniniform,  and  the  canines  which  are  long  and  sharp  are 
very  like  the  anterior  premolars,  but  have  their  outer  cusps 
much  longer.  The  inner  cusp  of  the  anterior  lower  premolar 
is  hardly  developed,  but  in  pm3  the  inner  cusp  and  posterior 
cingulum  is  more  pronounced,  and  in  pm4  it  is  yet  more 
strongly  expressed  :  they  are  all  single  rooted,  and  show 
the  relationship  of  the  canine  to  the  premolars  excellently 
well. 

The  upper  premolars,  especially  the  last,  have  roots  bifur¬ 
cated  near  their  tips,  but  have  not  three  roots.  The  bifur¬ 
cation  in  the  root  of  nq  takes  place  only  low  down,  in  m2 
lower  still,  and  m3  is  single  rooted  and  small,  so  that  the 
teeth  show  a  tendency  to  reduction. 

Of  the  upper  molars  the  first  two  are  three  rooted,  but  the 
third  is  hardly  even  bifurcated. 

All  Quadrumana  have  well  developed  milk  dentitions. 

Old  world  or  Catarrhine  monkeys  all  have  the  same 


dental  formula  as  man — 


9. 


o 


As  an  example  the  Macaque  monkey  may  be  taken.  The 
)  upper  and  lower  incisors,  but  especially  the  former,  are 
directed  obliquely  forwards,  and  the  lateral  incisors  are  very 


448 


A  MANUAL  OF  DENTAL  ANATOMY. 


much  smaller  than  the  centrals.  In  the  upper  jaw  a  con¬ 
siderable  interval  separates  the  incisors  from  the  canine, 
which  is  a  very  large  tooth,  somewhat  triangular  in  section, 
with  a  sharp  edge  directed  backwards,  and  with  a  deep 
groove  on  its  anterior  surface. 


roots,  as  are  also  the  true  molars  ;  the  latter  are  quadri- 
cuspid,  but  lack  the  oblique  ridge. 

The  lower  canine  is  a  sharp  and  powerful  tooth,  though 
it  is  very  much  smaller  than  the  upper;  the  first  lower 
premolar,  by  its  front  surface,  articulates  with  the  upper 
canine,  and  is  of  curious  form.  It  is  implanted  by  two 
roots,  but  the  anterior  root  is  produced  forwards,  so  that  the 
antero-posterior  extent  of  the  tooth  is  much  increased. 

The  apex  of  the  cusp  of  the  tooth  is  almost  over  the 
posterior  root,  and  from  this  point  the  crown  of  the  tooth 

O  Upper  and  lower  teeth  of  a  Monkey  (Macacus  nemestrinus,  male). 
The  length  and  sharpness  of  the  canines,  and  the  peculiar  form  of  the 
anterior  lower  premolar,  contrast  with  the  aspect  of  the  corresponding 
teeth  in  the  Anthropoid  Apes  or  in  Man. 


THE  TEETH  OF  PRIMATES. 


449 


slopes  obliquely  forwards  down  to  its  anterior  root.  This 
peculiarity  in  the  form  of  the  first  lower  premolar  is  eminently 
characteristic  of  the  baboons.  There  is  nothing  to  note  of 
the  second  premolar  save  that  it  is  implanted  by  two  roots, 
like  the  true  molars,  which  are  quadricuspid ;  of  them  the 
third  is  larger  than  the  first  two,  and  is  quinquicuspid. 

But  in  some  genera,  e.g.  Cercopithecus,  this  is  reduced  in 
size  and  is  tricuspid. 

There  is  considerable  difference  in  the  size  of  the  canine 
in  the  two  sexes,  that  of  the  male  being  very  much  the 
larger ;  this  difference  does  not  exist  in  the  deciduous  den¬ 
tition,  in  which  the  canines  are  relatively  small. 

The  Anthropoid  Apes  are  the  Gibbons  (Hylobates),  the 
Chimpanzee  (Simia  troglodytes,  or  Troglodytes  niger),  the 
Orang  (Simia  or  Pithecus  satyrus),  and  the  Gorilla  (Troglo¬ 
dytes  gorilla). 

Upon  the  whole  the  gibbons  are  the  lowest,  and  the 
gorilla  the  highest  of  the  anthropoid  apes,  which  are  all 
confined  to  tropical  areas.  Thus  the  gorilla  and  chimpanzee 
are  confined  to  tropical  Africa,  and  the  orang  is  limited  to  a 
part  of  the  Malay  archipelago.  The  gibbons  are  more 
widely  distributed  over  the  Malay  archipelago  and  tropical 
Asia. 

Although  upon  the  whole  the  gorilla  approaches  most 
nearly  to  man,  this  can  hardly  be  said  to  be  the  case  with 
its  dentition.  The  jaws  are  very  square,  and  there  is  a  large 
diastema  in  front  of  the  upper  canine,  which  in  the  male 
gorilla  is  of  great  size  and  strength,  its  top  descending  far 
below  the  level  of  the  alveolar  border  of  the  lower  jaw  when 
the  mouth  is  shut. 

In  the  lower  jaw  there  is  no  diastema,  but  the  teeth  are 
all  in  contact  with  one  another ;  the  first  of  the  premolars 
t  is  a  very  strong  pointed  cone,  showing  plainly  the  close 
relationship  between  canines  and  premolars  alluded  to  at  a 
previous  page. 


G  G 


450 


A  MANUAL  OF  DENTAL  ANATOMY. 


The  molars  increase  in  size  from  before  backwards,  the 
third  molars  attaining  to  a  very  large  size. 

Nevertheless,  though  the  teeth  are  coarser  and  stronger, 
there  is  a  general  resemblance  to  those  of  man. 

It  has  been  pointed  out  by  the  late  Professor  Rolleston  that 
the  canine  tooth  of  the  male  anthropoid  apes  is  a  little  later 
in  coming  into  place  than  in  the  female.  Thus  in  the  male 
chimpanzee  and  orang,  it  is  not  cut  until  after  the  third 


Fig.  197  P). 


molars  (wisdom  teeth)  are  in  place,  whereas  in  the  female 
it  follows  the  second,  but  precedes  the  third  molars.  The 
sexual  difference  in  the  canine  teeth  is  very  well  marked  in 
all  the  anthropoid  apes,  and  its  later  eruption  in  the  males 
is  explicable  both  upon  the  ground  that,  being  a  sexual 
weapon,  it  is  not  needed  prior  to  the  attainment  of  sexual 
maturity,  and  also  that  being  of  very  large  size  its  formation 
might  be  expected  to  take  a  longer  time.  No  such  difference 
pertains  to  the  milk  dentition,  in  which  the  order  of  eruption 
is  exactly  that  met  with  in  man. 

Dr.  Magitot  (Bulletin  de  la  Societe  d’Anthropologie  de 
Paris,  1869)  combats  the  idea  that  there  is  any  difference  in 

P)  Upper  and  lower  teeth  of  an  Anthropoid  Ape  (Simia  satyrus,  or 
Orang  Outan). 


THE  TEETH  OF  PRIMATES. 


451 


the  order  of  the  eruption  of  the  permanent  teeth  between 
man  and  the  anthropoid  apes,  but,  while  his  observations 
have  been  both  careful  and  widely  extended,  he  lays  much 
stress  upon  an  observation  made  upon  a  female  gorilla  skull, 
in  wdiich,  as  has  just  been  mentioned,  the  order  of  succession 
is  not  quite  the  same  as  in  the  male. 

In  a  specimen  of  a  New  World  Monkey  (Cebus  hypoleucus) 
I  have  found  m3  on  the  point  of  erupting,  whilst  the 
temporary  milk  molars  had  not  yet  been  shed,  and  its 
canine  was  not  yet  erupted. 

Prof.  Flower  says  in  general  terms  that  the  canines  are  the 
last  teeth  to  be  cut,  but  mentions  that  in  the  gibbons  they 
come  up  at  the  same  time  with,  or  even  precede,  the  third 
molar,  and  this  is  also  sometimes  the  case  in  the  orang. 

Giglioli  says  that  in  a  chimpanzee  the  order  is  the  same 
as  in  man,  but  that  in  a  male  gorilla  he  found  the  canines  and 
third  molar  erupting  simultaneously,  the  former  teeth,  how¬ 
ever,  taking  the  longest  time  to  fully  erupt. 

The  dentition  of  the  orang  approaches  tolerably  closely  to 
that  of  man,  and  the  points  of  resemblance  and  of  difference 
may  be  fairly  well  seen  in  the  accompanying  figure. 

The  central  upper  incisors  are  similar  to  those  of  man, 
but  are  larger;  the  laterals  are,  relatively  to  the  centrals, 
much  smaller,  and  are  very  caniniform  in  shape,  both  inner 
and  outer  angles  of  their  cutting  edge  being  sloped  off  to 
such  an  extent  that  a  central  pointed  cusp  remains,  in 
place  of  a  thin  cutting  edge.  The  canines  are  strong, 
pointed  teeth,  the  cingulum  and  the  ridge  joining  it  with 
the  apex  of  the  cusp  being  well  marked  upon  their  inner 
sides.  In  the  female  the  upper  canine  is  about  half  as 
long  again  as  any  of  the  other  teeth ;  in  the  male  it  is 
longer. 

The  first  bicuspid  is  a  little  more  caniniform  than  that 
of  man  ;  its  outer  cusp  is  long  and  pointed,  and  a  ridge 
unites  it  with  the  anterior  part  of  the  inner  cusp,  which  is 

g  g  2 


452 


A  MANUAL  OF  DENTAL  ANATOMY. 


feebly  pronounced  ;  the  second  is  a  blunter  and  broader 
tooth.  The  premolars  are  implanted  by  three  roots.  The 
molars  are  not  unlike  the  human  teeth  in  pattern. 

In  the  lower  jaw  the  incisors  are  large  and  stout ;  the 
canines  sharply  pointed,  with  a  well-marked  cingulum, 
and  a  well-marked  median  ridge  on  the  inner  side  of  the 
crown.  The  first  premolar  is  a  shorter,  stouter,  and 
blunter  copy  of  the  canine,  and  can  hardly  be  said  to 
have  an  inner  cusp.  In  the  second  premolar  the  inner 
cusp  is  as  high  as  the  outer,  and  the  cingulum  is  elevated 
both  before  and  behind  till  it  almost  forms  two  additional 
cusps,  but  both  have  two  distinct  roots  which  lie  anteriorly 
and  posteriorly  like  those  of  the  lower  molars. 

Indeed,  I  am  not  acquainted  with  any  dentition  which 
exemplifies  the  transition  from  incisors  to  canines,  from 
canines  to  premolars,  and  from  premolars  to  true  molars, 
better  than  that  of  the  orang. 

There  is  also  a  point  of  interest  about  the  lower  premolars 
which  may  be  noticed  here.  If  the  lower  first  premolar  of 
one  of  the  anthropoid  apes  be  examined  it  will  be  found 
that  its  posterior  root  occupies  the  whole  width  of  the 
alveolar  border,  but  the  anterior  root,  though  when  looked 
at  from  the  outside  it  does  not  greatly  differ,  when  looked  at 
from  above  is  found  to  be  of  much  less  width,  and  it  does  not 
extend  inwards  to  much  more  than  half  the  distance  reached 
by  the  posterior  root. 

There  is  a  form  of  abnormal  root  which  is  met  with  in 
the  first  lower  premolar  of  man,  of  sufficient  frequency 
of  occurrence  to  obviously  have  some  significance,  which 
consists  in  the  outer  border  of  the  root  towards  its  apex 
being  folded  forwards  and  inwards,  so  as  to  present  an 
approximation  to  a  double  root  at  the  end.  I  have  myself 
collected  eighteen  examples  of  this,  and  in  two  it  has  gone  to 
the  extent  of  a  second  small  anterior  root  being  completely 
formed. 


THE  TEETH  OF  PRIMATES. 


453 


Thus  we  have  as  a  comparatively  common  abnormality  a 
tendency  to  the  formation  of  two  roots,  one  anterior  and  the 

other  posterior,  and  in  every  single  instance  it  is  the 

% 

posterior  root  which  is  fully  developed,  and  the  anterior  root 
is  tending  to  be  formed  as  a  smaller  root,  on  the  outside 
quite  level  with  the  other,  but  not  extending  inwards  in 
the  direction  of  its  width  to  nearly  the  same  extent  as  the 
posterior  root.  In  fact  it  is  trying  to  parallel  the  state 


of  things  which  is  constant  in  most  anthropoid  apes,  and  is 
hardly  explicable  on  any  other  hypothesis  than  that  it  is  a 
reversion,  for  in  a  reduced  dentition  like  that  of  a  xanthocroic 
man  it  is  not  conceivable  that  there  should  be  a  tendency 
to  the  development  of  a  second  root  to  the  first  premolar  as 
a  commencement  of  a  new  order  of  things. 

The  lower  molars  resemble  those  of  man,  save  that  their 
surface  is  marked  by  that  finely  wrinkled  pattern  which  is 
common  to  all  the  unworn  teeth  of  the  orang.  One  is 
struck  by  the  great  backward  elongation  of  the  jaws,  by 
their  squareness,  by  the  parallelism  of  the  two  sides, 

P)  Lower  premolar  (human).  In  the  right-hand  figure  a  second  (anterior) 
root  is  in  process  of  formation  by  a  folding  round  of  the  flattened  end  of 
the  root ;  in  the  left  hand  figure  it  has  .attained  to  being  a  distinct  root. 


454 


A  MANUAL  OF  DENTAL  ANATOMY. 


which  converge  slightly  at  the  back,  and  by  the  large  size 
of  the  teeth  in  proportion  to  the  bulk  of  the  whole  animal. 


Fig.  199  (*). 


Fig.  200  (2). 


Fig.  201  (3). 


The  large  size  of  the  canines  being  in  a  measure  a  sexual 
character,  is,  as  is  so  often  the  case,  not  very  noticeable  in 
the  young  animal the  two  accompanying  illustrations  of 

(b  Skull  of  a  young  male  Orang.  The  upper  canine  does  not  nearly 
reach  to  the  lower  alveolar  border. 

(")  Skull  of  adult  male  Orang,  in  which  the  canine  is  largely  developed. 

(*)  Side  view  of  skull  of  an  idiot. 


THE  TEETH  OF  PRIMATES. 


455 


a  young  and  an  adult  male  orang  may  serve  to  show  this,  as 
well  as  some  other  differences  developed  by  age. 

A  peculiarity  of  the  orang  lies  in  the  enormous  length 
of  the  roots  of  its  teeth  ;  this  is  not  shared  by  the  gorilla, 
the  roots  of  whose  teeth  are  proportionately  shorter,  and 
the  chimpanzee  has  roots  far  shorter  and  feebler  than  either. 

Looking  at  the  palatine  surface  of  the  jaws  of  an  orang, 

Fig.  202  (l). 


the  front  of  the  mouth  is  squarish,  and  the  premolars  and 
molars  stand  nearly  in  a  straight  line,  not,  however,  strictly 
parallel  with  those  of  the  opposite  side,  as  they  approximate 
at  the  back,  the  third  molars  being  nearer  together  than  the 
premolars.  In  the  gorilla  the  two  sides  of  the  “  arch  ”  are 
parallel,  and  in  the  chimpanzee  they  are  also  nearly  parallel, 
with  a  slight  approximation  at  the  back. 

The  teeth  of  the  Chimpanzee  are  not  very  powerfully 
developed,  and  the  third  molars  are  a  good  deal  smaller  than 
the  other  teeth ;  the  lower  premolars  also  have  their  two 
roots  more  or  less  fused. 

There  would  appear  to  be  a  great  deal  of  variability  about 
the  articulation  of  the  upper  and  lower  teeth  in  the  higher 
apes.  Thus  in  the  British  Museum  there  are  three  orangs 

(!)  Lower  Teeth  of  Orang.  Figure  of  jaws  from  which  bone  has  been 
removed  exposing  the  roots  of  the  teeth  to  their  ends. 


456 


A  MANUAL  OF  DENTAL  ANATOMY. 


which  are  distinctly  underhung,  and  several  whose  incisors 
present  an  “edge  to  edge ’’bite.  There  are  also  three 
underhung  chimpanzees,  as  well  as  one  which  is  underhung 
in  the  milk  dentition,  a  thing  exceedingly  rare  in  man. 
There  is  also  an  underhung  gorilla,  and  in  the  museum  of 
the  Odontological  Society  there  is  a  gorilla’s  skull  in  which 
the  lower  jaw  contains  two  supernumerary  teeth  buried  in  the 
substance  of  the  ascending  ramus,  with  their  crowns  looking 
upwards,  close  to  the  foramen  where  the  inferior  dental  nerve 
and  vessels  enter  the  bone  (Odonto.  Soc.  Transac.,  voh  xix., 
1887). 

The  differences  which  serve  to  distinguish  the  dentition 
of  the  most  anthropomorphic  apes  from  that  of  man  are 
mainly  these.  Relatively  to  the  size  of  the  cranium,  and  of 
the  whole  creature,  the  teeth  and  jaws  are  very  much  larger 
in  all  their  dimensions  ;  hence  the  creatures  are  progna¬ 
thous,  and  the  facial  angle  small,  even  when  compared 
with  the  jaws  and  cranium  of  an  idiot.  As  might  be  ex¬ 
pected  this  difference  is  not  so  great  in  the  young  as  in  the 
adult  animal. 

In  place  of  the  teeth  being  arranged  in  a  sweeping  curve, 
the  jaws  are  squarish,  the  incisors  being  arranged  in  some¬ 
thing  approaching  to  a  straight  line  between  the  two  great 
outstanding  canines,  behind  which  the  premolar  and  molar 
series  run  in  straight  lines,  converging  somewhat  as  they  go 
backward.  There  is  a  “  diastema  ”  (l)  or  interval  in  front  of 
the  upper  canine,  into  which  the  point  of  the  lower  canine 
passes,  when  the  mouth  is  closed.  Both  the  greater  square¬ 
ness  of  the  jaws,  and  the  existence  of  a  diastema,  are  direct 
results  of  the  great  size  of  the  canines,  and  are  consequently 
not  marked  in  young  specimens. 

The  upper  premolars  are  implanted  by  three  roots,  the 
lower  by  two  roots,  just  like  the  true  molars,  and  the  pre- 

(b  Something  approaching  to  a  diastema  is  said  to  have  been  observed 
by  Vogt  and  broca  in  early  European  skulls. 


THE  TEETH  OF  PRIMATES. 


457 


molars  when  unworn  partake  more  of  the  pointed  character 
than  they  do  in  man. 

Fig.  203  (*). 


Fig.  204  (2). 


The  wisdom  teeth  present  the  same  pattern  of  grinding 

(*)  Upper  teeth  of  a  Caffir.  The  oblique  riclge  of  the  upper  molar  is  dis¬ 
tinct,  not  only  upon  the  first  and  second,  but  also  upon  the  third  molar  or 
wisdom  tooth,  which  in  this  skull  has  the  normal  three  roots  well  marked. 

(2)  Lower  jaw  of  a  Caffir,  in  which  the  quinquicuspid  form  of  the  first 
and  third  molars  is  well  seen,  it  being  somewhat  less  strongly  indicated  in 
the  second  molars.  .  . '  '  '  -  ‘  ' 


458 


A  MANUAL  OF  DENTAL  ANATOMY . 


surface,  are  larger  than  the  other  molars  in  the  gorilla 
and  the  orang,  and  there  is  abundant  space  for  them,  so 
that  they  play  an  important  part  in  mastication.  The 
molar  teeth  of  these  apes  are  also  squarer,  their  cusps 
sharper  and  longer,  and  the  characteristic  patterns  more 
strongly  pronounced,  than  in  man.  Moreover  the  intermax¬ 
illary  bone  is  more  largely  developed,  and  the  intermaxillary 
suture  remains  distinct  through  life. 

Anthropidse. — In  passing  from  the  highest  of  the  apes 
to  the  lowest  of  mankind,  there  is  a  sudden  change  in  the 
character  of  the  dentition ;  but  while  it  cannot  but  be 
admitted  that  there  is  a  gap,  yet  the  differences  are  rather 
of  degree  than  of  kind. 

Even  in  the  lowest  of  human  races  the  facial  angle  is 
greater,  that  is  to  say,  they  are  much  less  “  prognathous  ” 
than  the  apes,  and  the  upper  and  lower  incisors  are  more 
nearly  vertical  in  position,  not  meeting  one  another  at  such 
an  angle  as  in  the  apes.  Mr.  Perrin  (Monthly  Review  Dent. 
Surgery,  1872)  states  that  in  a  gorilla  skull  there  is  an  inch 
of  bone  in  front  of  the  anterior  palatine  foramen :  in  a  negro 
half  an  inch,  and  in  a  Greek  skull  it  was  close  behind  the 
incisors. 

It  is  generally  said  that  in  man  the  molars  decrease  in 
size  from  before  backwards  ;  that  is  to  say,  that  the  first 
molar  is  the  largest,  while  in  anthropoid  apes,  with  the 
exception  of  the  chimpanzee,  the  contrary  is  the  case. 
Though  this  is  on  the  whole  true,  it  requires  some  qualifi¬ 
cation  :  thus  in  certain  lower  races,  such  as  the  Australian 
blacks,  the  second  and  third,  molars  are  not  smaller  than 
the  first. 

There  is  no  diastema ;  no  sexual  difference  in  dentition ; 
no  tooth  projecting  beyond  its  fellows,  and  the  teeth  are 
arranged  in  an  unbroken  arch.  The  premaxillary  bones 
become  fused  with  the  superior  maxillary  early  in  life, 
whereas  in  the  Quadrumana  they  remain  distinct. 


THE  TEETH  OF  PRIMATES. 


459 


In  general  terms  it  may  be  said  that  the  dentition  of  the 
lower  races  of  mankind  differs  from  that  of  the  higher  in  the 
following  particulars  :  the  arch  is  not  so  rounded,  but  is 
squarer  in  front ;  the  teeth  are  larger,  and  are  disposed 
with  greater  regularity  ;  the  wisdom  tooth  has  ample  space 
to  range  with  the  other  teeth,  and  is  a  characteristic  upper 
or  lower  molar,  the  pattern  of  its  grinding  surface  (quadri- 
cuspid  if  it  be  an  upper,  quinquicuspid  if  it  be  a  lower 
tooth)  and  the  disposition  of  its  roots  corresponding  with  the 
first  and  second  molars,  which  do  not  greatly  exceed  it  in 
size.  Specimens  of  negro  skulls  may  be  found  in  which 
there  is  scanty  room  for  the  wisdom  tooth,  and  in  which 
consequently  it  is  a  little  stunted  in  its  development :  on 
the  other  hand,  plenty  of  well  formed  and  well  placed 
wisdom  teeth  may  be  picked  out  of  European  mouths, 
though  as  a  rule  the  wisdom  tooth  is  much  smaller  than 
the  other  molars,  does  not  bear  the  characteristic  pattern 
of  cusps  and  grooves,  has  its  roots  connate,  and  it  is  not  very 
infrequently  a  mere  rudimentary  peg.  The  stunted  develop¬ 
ment  of  the  wisdom  tooth  would  seem  to  be  a  consequence 
of  want  of  space  during  its  formative  period ;  the  upper 
wisdom  tooth  is  especially  apt  to  be  cramped  in  this  way. 

There  is  some  little  evidence  that  the  wisdom  tooth  is  in 
process  of  disappearance  from  the  jaws  of  civilized  races  : 
in  anthropoid  apes  the  wisdom  tooth  is  nearly  or  quite  as 
large  as.  the  other  molars,  and  shows  no  variability,  whilst 
it  comes  into  place  almost  simultaneously  with  the  canine  : 
in  the  lowest  races  of  mankind  the  wisdom  tooth  appears  to 
vary  but  little,  is  of  large  size,  and  is  seldom  misplaced ;  in 
highly  civilised  races  it  is  very  variable  in  size,  form,  and  in 
the  date  of  its  appearance,  is  often  misplaced,  and  is  not 
uncommonly  quite  rudimentary.  It  seems  to  be  a  legitimate 
inference  that  a  further  modification  of  the  race  in  the  same 
direction  will  result  in  the  disappearance  of  the  wisdom 
tooth  altogether. 


460 


A  MANUAL  OF  DENTAL  ANATOMY. 


Some  exception  must  however  be  taken  to  such  general 
statements :  thus  the  Esquimaux  not  uncommonly  have  the 
wisdom  teeth  small  and  sometimes  crowded  out  of  place  ; 
and  amongst  the  African  races  instances  on  the  one  hand  of 
the  wisdom  teeth  being  small,  and  on  the  other,  of  fourth 
true  molars  existing,  are  to  be  met  with. 

Nevertheless,  for  the  present,  a  case  in  which  the  wisdom 
teeth  are  very  small  can  hardly  be  called  a  typical  well- 
developed  European  mouth. 

In  many  low  races  (Bosjesman,  Negro,  Australian,  New 
Caledonian,  Caffir)  the  second  lower  molar  has  five  cusps, 
just  like  the  first :  this  is  so  in  the  anthropoid  apes,  but  in 
European  races  the  fifth  cusp  is  generally  wanting  in  the 
second  lower  molar. 

It  is  believed  by  Professor  Cope  that  the  quadri-tuber- 
culate  molar  of  European  races  shows  a  tendency  to 
revert  to  a  tri-tuberculate  type  such  as  is  seen  in  Eocene 
lemurs. 

It  is  not  a  little  interesting  thus  to  find  that  the  differ¬ 
ences  which  serve  to  distinguish  the  teeth  of  the  lowest 
savage  from  those  of  a  European,  are  to  a  certain  extent 
the  same  with  those  that  mark  the  step  from  a  Quadru- 
manal  to  a  human  dentition,  though  of  course  the  diver¬ 
gence  of  the  dentition  of  the  sa\  age  from  that  of  the  ape  is 
far  greater  than  is  that  of  the  European  from  the  lowest 
savage. 

It  is  very  possible  that  the  larger  development  of  the 
jaws  of  the  savage  may  be  simply  due  to  the  harder  work  to 
which  they  are  put  while  he  is  growing  up.  And  after  the 
attainment  of  adult  proportions,  the  teeth  of  such  a  man 
become  greatly  worn  down  by  reason  of  the  hard  and  often 
gritty  nature  of  his  food. 

It  was  pointed  out  by  Mr.  Mummery,  in  a  very  instructive 
paper  (“  Transactions  of  the  Odontological  Society,”  vel.  ii., 
new  series,  1869),  that  destructive  wearing  down  of  the 


THE  TEETH  OF  PRIMATES. 


461 


teeth  was  of  very  common  occurrence  amongst  rude  (*)  races, 
while  the  contrary  is  true  of  highly  civilised  races ;  this  was 
very  likely  due  to  the  admixture  of  earth  and  other  foreign 
matter  with  the  food.  And,  furthermore,  that  the  occurrence 
of  dental  irregularities,  due  to  an  insufficient  size  of  the 
arches,  was  comparatively  speaking  unknown  among  the 
ruder  races,  whilst  it  has  been  common  amongst  peoples  of 
more  luxurious  habits  for  a  long  period  of  time. 

The  range  of  variation  in  the  size  of  the  jaws  of  healthy, 
otherwise  well-developed  adults  is  great  :  thus  the  smallest 
jaw  (occurring  in  a  man  of  stout  build,  above  middle  height) 
with  which  I  am  acquainted  measures  in  width  only  li  inch, 
and  in  length  from  back  to  front  If  inch  ;  avhile  the  largest 
(occurring  in  a  gentleman  of  lesser  stature  ;  of  Basque  ex¬ 
traction,  moreover,  which  makes  it  the  more  striking)  (3) 
measures  no  less  than  2|  inches  in  width  and.  2J  inches  in 
length  :  and  even  larger  dimensions  are  recorded  in  the 
“Dental  Cosmos”  of  September,  1876 ;  the  width  being  taken 
between  the  centre  of  the  alveolar  borders  at  the  position  of 
the  wisdom  teeth,  and  the  length  being  measured  on  a  line 
drawn  from  the  incisors  to  another  line  joining  the  two 
wdsdom  teeth. 

On  the  whole,  it  must  be  said  that  there  are  fewer 
constant  differences  between  the  teeth  of  the  various  races 
of  mankind  than  might  have  been  d  priori  expected ;  in  fact, 
we  may  almost  say  that  the  teeth  of  savage  man  are  pretty 
much  what  we  should  look  upon  as  an  exceedingly  perfectly 
formed  set  of  teeth  if  we  were  to  see  them  in  the  mouth  of 
a  European. 

Prof.  Flower  (Journ.  Anthropol.  Instit.,  March,  1885), 

(1)  To  those  races  mentioned  by  Mr.  Mummery  may  be  added  the 
mound- builders  of  North  America,  whose  teeth  were  always  worn  down  to 
an  excessive  extent. 

(2)  Magitot  (Bullet,  dc  la  Soc.  Anthropol.  de  Paris,  1869)  says  : — “Les 
Basques,  par  exemple,  remarquables  par  la^petitesse  extreme  de  leursdents.” 


462 


A  MANUAL  OF  DENTAL  ANATOMY. 


has  investigated  the  relation  of  the  size  of  the  teeth  to  that  of 
the  skull  very  closely,  with  the  result  of  bringing  out  certain 
race  distinctions.  As  measures  for  comparison  he  takes  the 
length  of  the  cranio-facial  axis,  measured  from  the  front  edge 
of  the  occipital  foramen  to  the  naso-frontal  suture,  and  the 
length  from  the  front  of  the  first  premolar  to  the  back  of  the 
third  molar  in  situ.  His  “  Dental  Index  ”  is  arrived  at  thus 

^  .  i  T  j  Length  of  Teeth  x  100 

Dental  Index  =  - - 5 - - - _ -  ; 

Cranio-facial  axis 

This  gives  figures  ranging  from  42  (microdont),  43  (meso- 
dont),  44  and  upwards  (megadont). 

As  in  the  female  the  skull  is  smaller  whilst  the  teeth  are 
the  same,  a  slightly  higher  index  is  arrived  at  in  them : 

The  Microdont  races  are— 


European. 

Egyptian. 

British. 

Polynesian. 

The  Mesodont  are — 

Chinese. 

Malays. 

American  Indian. 

N  egroes. 

And  the  Megadont — 

Melanesians. 

Australian. 

Andamanese. 

Tasmanian. 

As  to  this  classification  it  is  to  be  remarked  that  the  teeth 
of  Polynesians  are  actually  larger  than  those  of  Europeans, 
but  the  cranio-facial  axis  is  of  extreme  length,  so  that  the 
index  is  reduced ;  this  is  also  the  case  with  the  American 
Indians,  whilst  the  Andamanese  are  brought  into  the 
Megadont  series  by  the  relative  size  of  teeth  to  the  basis 
cranii,  though  in  this  small  people  the  teeth  are  actually 
small. 

The  dental  index  of  Megadont  races  being  from  44-47, 
that  of  the  chimpanzee  is  little  more  than  the  highest  of 


I 


THE  TEETH  OF  PRIMATES.  463 


these,  namely  47 -9,  whilst  the  orang  rises  to  55,  and  the 
gorilla  to  54,  but  in  the  gibbon  the  index  is  as  low  as  41  *7. 
It  is,  however,  the  opinion  of  the  African  traveller  Mr. 
Stanley,  that  the  teeth  of  African  races  vary  in  accordance 
with  the  build  of  the  individual,  and  particularly  with  the 
size  of  the  jaws,  such  small  races  as  the  Somalis  having 
small  teeth.  It  does  not  appear,  however,  that  these  impres¬ 
sions  are  based  upon  actual  exact  measurement,  but  only 
upon  general  appearance.  He  mentions  that  many  of  the 
races  who  show  no  regard  for  cleanliness  otherwise,  assiduously 
clean  their  teeth. 

The  dental  formula  of  man  is  of  course 


But  the  question  has  recently  been  raised  as  to  which  of  the 
incisors  of  the  typical  mammalian  dentition  are  wanting. 

Prof.  Sir  W.  Turner  (“  Journ.  Anat.  and  Physiol.,”  1885), 
and  Mr.  Andrew  Wilson  (“British  Deni.  Assoc.  Journ.,”  1885), 
bring  forward  a  certain  amount  of  evidence  which  raises  a 
doubt  as  to  whether  it  is  not  i2  which  is  missing  in  man.  In 
cases  of  cleft  palate  the  cleft  is  often  demonstrably  not  in 
the  line  of  the  intermaxillary  suture  but  well  within  it,  and 
there  is  often  an  incisor-like  tooth  on  the  canine  side  of  the 
cleft  as  well  as  two  on  the  other  side  of  it,  a  so-called  “pre¬ 
canine.”  The  frequency  of  occurrence  of  this  tooth,  and  a 
study  of  those  cases  in  which  the  incisors  are  present,  lend 
some  support  to  the  idea  that  it  is  i2  which  is  lost  in  the 
ordinary  human  dentition. 


CHAPTER  XI. 


THE  TEETH  OF  MARSUPIALIA. 

The  great  sub-class  of  Marsupials,  consisting  of  animals  very 
sharply  marked  off  from  placental  Mammals  by  many  striking 
peculiarities,  and  amongst  others,  by  the  very  helpless  condition  in 
which  the  foetus  is  born,  was  once  very  widely  distributed  over  the 
globe.  Now,  however,  Marsupials  are  numerous  only  in  Australia, 
where  they  are  almost  the  sole  representatives  of  the  Mammalian 
class  ;  there  are  a  few  Marsupials  elsewhere,  as  in  America 
(Opossums)  and  New  Guinea ;  but  there  are  no  Marsupials  in 
Europe,  most  parts  of  Asia,  and  Africa. 

The  Marsupials  of  America  are  all  Opossums  (DldelpMdce) ,  and 
this  family  is  not  represented  in  Australia.  There  is  evidence  to 
indicate  that  the  Marsupials  of  America  have  nothing  at  all  to  do 
with  the  Australian  Marsupials,  but  were  derived  from  a  different 
source,  at  the  time  when  Marsupials  abounded  all  over  Europe. 

The  Marsupials  of  Australia  almost  monopolise  that  country  ; 
thus  Mr.  Wallace  says  of  it  :  u  The  Australian  region  is  broadly 
distinguished  from  all  the  rest  of  the  globe  by  the  entire  absence 
of  all  the  orders  of  non-aquatic  mammalia  that  abound  in  the  old 
world,  except  two — the  Winged  Bats  ( Chiroptera ),  and  the  equally 
cosmopolitan  Rodents.  Of  these  latter,  however,  only  one  family  is 
represented — the  Muridse — (comprising  the  Rats  and  Mice),  and 
the  Australian  representatives  of  these  are  all  of  small  or  moderate 
size — a  suggestive  fact  in  appreciating  the  true  character  of  the 
Australian  fauna. 

“  In  place  of  the  Quadrumana,  Carnivora,  and  Ungulates,  which 
abound  in  endless  variety  in  all  the  other  zoological  regions  under 
equally  favourable  conditions,  Australia  possesses  two  new  orders 
or  sub-classes,  Marsupialia  and  Monotremata,  found  nowhere  else 
in  the  globe,  except  a  single  family  of  the  former  in  America. 

“  The  Marsupials  are  wonderfully  developed  in  Australia,  where 
they  exist  in  the  most  diversified  forms,  adapted  to  different  modes 
of  life.  Some  are  carnivorous,  some  herbivorous,  some  arboreal, 
others  terrestrial.  There  are  insect-eaters,  root-gnawers,  fruit- 
eaters,  honey-eaters,  leaf  or  grass-feeders. 


THE  TEETH  OF  MA  RS  JJ FI  A  LI  A . 


465 


“  Some  resemble  wolves,  others  marmots,  weasels,  squirrels,  flying 
squirrels,  dormice,  or  jerboas. 

“  They  are  classed  in  six  distinct  families,  comprising  about  thirty 
genera,  and  subserve  most  of  the  purposes  in  the  economy  of  nature 
fulfilled  in  other  parts  of  the  world  by  very  different  groups  ;  yet 
they  all  possess  the  common  peculiarities  of  structure  and  habits 
which  show  that  they  are  members  of  one  stock,  and  have  no  real 
affinity  with  the  old-world  forms,  which  they  often  outwardly 
resemble.” — “  Geographical  Distribution  of  Animals,”  p.  391. 


I  have  quoted  this  passage  from  Mr.  Wallace,  because 
much  of  it  is  applicable  to  the  teeth. 

In  Australia,  the  present  home  of  the  marsupials,  repre. 
sentative  species  abound  ;  that  is  to  say,  widely  different 
though  the  animals  really  are,  there  are  many  genera  and 
species  which  have  the  habits  of,  and,  as  it  were,  fill  the 
place  of  such  creatures  as  the  Carnivora  and  Insectivora  and 
Rodents  amongst  the  placental  mammalia.  And  not  only 
do  they  possess  something  of  their  habits  and  external  con¬ 
figuration,  but  in  those  characteristic  structures  which  are 
subservient  to  the  creature’s  immediate  wants,  the  marsupial 
representatives  closely  mimic  the  more  highly  organised 
placental  mammals.  Thus  the  teeth  of  an  insect-eating 
marsupial  very  closely  resemble  those  of  a  true  Insectivore, 
though  retaining  certain  eminently  marsupial  characters  ; 
in  the  same  way  the  dentition  of  the  marsupial  Thylacine 
mimics  that  of  a  dog  (compare  Figs.  206  and  207). 

And  although  marsupial  dentitions  do  vary  very  much, 
yet  there  are  many  transitional  forms  by  which  we  are  some¬ 
times  able  to  trace  the  successive  modifications  through 
which  extreme  divergence  has  been  ultimately  attained. 

Just  as  we  ascribe  to  placental  mammals  the  formula — 

3  14  3 

i  o  c  w  P  ~r  m  w  =  44 


as  the  typical  or  parent  dental  formula,  so  recent  marsupials 
possess  the  following — 


H  H 


466 


A  MANUAL  OF  DENTAL  ANATOMY. 


Though  no  living  marsupial  has  more  than  three  pre¬ 
molars,  it  may  he  presumed  that  four  was  the  original 
number,  as  in  placental  mammals,  and  Mr.  Oldfield  Thomas 
has  found  in  Dasyurus  and  in  Phascologale  dorsalis  a  fourth 
tooth,  in  the  position  of  pm2 ;  he  infers,  therefore,  that  it  is 
pm2  which  has  been  lost  by  recent  marsupials,  and  further 
points  out  that  a  marked  gap  exists  in  this  situation  in 
Didelphys,  Perameles,  and  others.  In  several  of  the  earlier 
fossil  marsupials,  e.g.,  Triconodon,  Ctenacodon,  Plagiaulax, 
and  others,  there  are  four  premolars  and  four  true  molars. 

The  marsupials  are  grouped  into  : — 

(i.)  Teeth  with  definite  roots. 

3 

(a.)  Diprotodonts,  i  The  central,  upper,  and 

the  lower  incisors,  are  large  and  trenchant, 
the  canines  small  or  absent :  e.g.,  Macropus 
and  Phalangista. 

(b.)  Polyprotodont. — Teeth  rooted,  incisors  nu¬ 
merous,  small  and  subequal ;  canines  large, 
and  molars  strongly  tuberculated :  e.g., 

Didelphys. 

(ii.)  Teeth  all  of  persistent  growth  :  e.g.,  Phascolomys 
(Wombat). 

Though  the  total  number  of  teeth  is  the  same  as  in 
placental  mammals,  the  marsupial  has  only  three  premolars 
and  has  four  true  molars.  The  premolars  (false  molars) 
differ  from  the  true  molars  in  the  greater  simplicity  of  their 
crowns,  just  as  in  most  placental  mammals;  but,  although, 
looking  at  the  complete  adult  dentitions,  no  hesitation  would 
be  felt  in  classing  the  teeth  under  the  heads  of  premolars 
and  true  molars,  yet  there  is  a  curious  anomaly  in  the  suc¬ 
cession  of  the  teeth  which  applies  to  the  whole  of  the  sub¬ 
class  Marsupialia,  and  to  some  e.xtent  invalidates  the  defini¬ 
tion  of  “  premolar  ”  as  applied  to  their  teeth.  Only  one  of 


THE  TEETH  OF  MARS UFIALIA. 


467 


the  premolars  ( the  hindmost)  has  vertically  displaced  a  milk 
tooth ;  indeed,  the  whole  milk  dentition  of  marsupials  con¬ 
sists  of  four  milk  molars  (one  on  each  side  of  each  jaw), 
there  being  no  milk  incisors  nor  canines  in  any  known 
marsupial.  It  is  further  pointed  out  by  Professor  Flower, 
who  was  the  first  to  fully  describe  these  peculiarities  in  the 
succession  of  marsupial  teeth  (“  Phil.  Trans.,”  1867),  that  the 
extent  to  which  the  solitary  milk  molar  is  developed  varies 
much  in  the  different  families ;  no  trace  of  any  succession 
has  been  observed  in  the  Wombat;  in  the  Thylacine  (a  dog¬ 
like  creature)  the  small  milk  molar  is  calcified,  but  is 
absorbed  or  shed  prior  to  any  other  teeth  being  erupted  ; 
whilst  in  the  Kangaroos  it  is  retained  till  a  much  later 
period  (see  page  478),  and  in  the  Kangaroo  Rat  (Hyp- 
siprymnus)  the  milk  molar  has  not  yet  given  place  to  its 
successor  at  the  time  when  the  last  permanent  molar  has 
come  into  place,  so  that  it  for  a  long  time  ranges  with  the 
other  teeth  and  does  work. 

This  subject  has  been  further  investigated  by  Mr.  Oldfield 
Thomas,  who  has  found  that  the  Dasyuridae  present  the  same 
milk  dentition  as  the  other  families,  that  is  to  say,  that 
some  have  a  well-developed  milk  molar,  and  that  it  occurs 
in  various  phases  of  reduction,  some  having  none  at  all 
(“Phil.  Trans.,”  1887).  This  author  writing  of  Phascolo- 
gale,  one  of  the  Dasyuridse,  says  : — 

“  The  normal  state  of  a  member  of  this  group  is  to  have 
three  well-developed  premolars,  the  last  one  of  which  has  a 
milk  predecessor.  Then  a  tooth  reduction  has  taken  place, 
all  of  which  has  fallen  upon  what  is  evidently  a  peculiarly 
plastic  tooth,  i.e.,  pm4,  and  this,  with  the  milk  tooth  pre¬ 
ceding  it,  has  been  decreased  in  various  degrees  and  in  the 
end  suppressed,  as  in  the  allied  genera  Dasyurus  and  Sarco- 
philus.” 

Those  species  which  have  a  large  pm4  have  preceding  it  a 
tricuspid  milk  tooth,  but  as  pm4  gets  reduced,  the  milk 

h  h  2 


468 


A  MANUAL  OF  DENTAL  ANATOMY. 


tooth  preceding  it  is  reduced  still  faster  till  it  quite  aborts  : 
even  then  the  pm4  presents  the  peculiarity  of  being  erupted, 
and  indeed  not  being  calcified,  until  later  than  the  other 
teeth. 

The  question  whether  the  tooth  change  of  the  marsupials 
is  the  remnant  of  a  more  complete  change  in  an  ancestral 
form,  or  is  the  dawning  of  a  more  complete  change,  is  dis¬ 
cussed  at  length  by  Mr.  Oldfield  Thomas. 

That  it  is  the  first  formation  of  a  change  he  holds  strongly, 
mainly  because  the  marsupials  are  at  a  lower  stage  of  evolu¬ 
tion,  and  so  it  would  be  unlikely  that  they  had  once 
evolved  a  change,  and  then  evolved  it  away  again,  seeing 
that  is  clearly  useful  to  placental  mammals — because  five 
out  of  the  six  marsupial  families  have  precisely  the  same 
amount  of  tooth  change,  which  would  be  unlikely  if  it  were 
an  atavism — and,  because  no  fossil  marsupials  present  any 
indication  of  a  fuller  change,  but  have  just  the  same. 

This  peculiarity  of  the  possession  of  a  single  milk  tooth 
was  fully  established  even  in  Mesozoic  times,  as  is  exempli¬ 
fied  in  Triaoanthodon  and  other  Mesozoic  marsupials. 

Mr.  Oldfield  Thomas  suggests  as  an  explanation,  that 
there  first  took  place  a  retardation  of  a  back  permanent 
tooth,  perhaps  useful  for  “ packing”  purposes  in  a  jaw  as 
yet  small,  and  that  when  the  retardation  had  gone  to  a  cer¬ 
tain  point,  a  milk  tooth  was  developed  to  fill  the  gap  in  the 
series  which  would  otherwise  have  existed. 

It  is  difficult  to  obtain  very  young  marsupials,  and 
material  for  the  complete  elucidation  of  the  subject  is 
wanting  ;  but  I  have  had  the  opportunity  of  making  sections 
of  the  jaws  of  several  young  specimens  (Perameles  and  Hal- 
maturus),  taken  from  the  pouch  by  my  friend  Prof.  Moseley, 
and  I  have  not  so  far  succeeded  in  finding  any  uncalcified 
germs  or  other  indications  of  any  more  teeth  of  a  milk 
dentition. 

A  further  peculiarity  of  the  marsupials  is  the  structure  of 


THE  TEETH  OF  MARS  UP  I  A  LI  A . 


469 


(l)  Enamel  and  dentine  of  a  Kangaroo  (ALacropus  major). 

The  dentinal  tubes  in  the  dentine  (A)  are  furnished  with  numerous  shor 
branches  at  the  line  of  juncture  with  the  enamel  ;  they  are  dilated,  and  a 
little  bent  out  of  their  course,  while  beyond  the  dilatation  they  pass  on 
through  about  two-thirds  of  the  thickness  of  the  enamel  in  a  straight 
course  and  without  branches.  Only  a  part  of  the  whole  thickness  of  the 
enamel  is  shown  in  the  figure.  B.  Enamel  penetrated  by  the  tubes. 
C.  Individual  dentinal  tube. 


c-H 


470 


A  MANUAL  OF  DENTAL  ANATOMY. 


their  enamel,  which  is  penetrated  by  the  dentinal  tubes. 
My  father,  some  years  ago,  described  and  figured  the  teeth 
of  a  large  number  of  marsupial  genera  (“Phil.  Trans.,” 
1850),  and  found  that  although  in  the  different  families  the 
tube  system  of  the  enamel  varied  in  its  richness  and  in  the 
depth  to  which  the  tubes  penetrated,  yet  it  was  con¬ 
spicuously  present  in  the  whole  class,  with  the  sole  exception 
of  the  Wombats,  in  whom  nothing  of  the  kind  is  to  be  found. 
Prof.  Moseley’s  specimens  have  afforded  to  me  the  opportu¬ 
nity  of  studying  the  development  of  this  tubular  enamel,  and 
the  result  of  my  investigations  will  be  detailed  elsewhere  ; 
but  it  may  be  mentioned  that  the  formation  of  the  enamel 
tube  appears  to  be  precisely  analogous  to  that  of  a  dentine 
tube,  and  at  a  certain  period  the  enamel  cells  have  appended 
to  them  long  processes  like  the  dentinal  fibres.  The  dila¬ 
tation  noticeable  at  the  boundary  line  of  the  enamel  and 
the  dentine  (see  Fig.  205)  is  a  kind  of  clumsy  joint  brought 
about  by  the  coalescence  at  this  point  of  the  tube-forming  cells 
- — on  the  one  side  odontoblasts,  on  the  other  enamel  cells. 

There  exists  one  genus  of  flesh- eating  marsupials  whose 
ferocity  is  such  as  to  have  gained  for  them  the  names  of 
wolf  and  tiger,  while  the  resemblance  of  the  head  to  that  of 
a  dog  has  given  origin  to  the  popular  name  of  “  dog-headed 
opossums  ”  (*). 

The  resemblance  to  the  dog  in  dentition  is  even  more 
close  than  in  external  form  :  whilst  retaining  certain  mar¬ 
supial  attributes,  the  teeth  of  the  Thylacine  are,  so  far  as 
their  working  capabilities  go,  almost  exactly  like  those  of  the 
dog.  The  dental  formula  is — 

.413  4 

i  c  p  -  m 

3  1  1  3  4 

The  incisors  are  small,  close  set,  and  sharp  edged,  the 

(l)  It  has  of  course  no  real  relationship  to  the  true  opossums,  which  are 
not  found  in  Australia. 


THE  TEETH  OF  MA  RS  UP  I  A  LI  A . 


471 


outermost  being  somewhat  caniniform.  The  canines  are 
stout,  pointed  teeth,  not  quite  so  long  relatively  as  those 
of  a  dog.  The  premolars  are  conical  teeth,  implanted  by 

Fig.  206  (*). 


Fig.  207  (2). 


two  roots,  and  very  similar  to  those  of  the  dog ;  they  are 
followed  in  the  upper  jaw  by  four  molars,  increasing  in  size 

(!)  Upper  and  lower  teeth  of  the  Thylacine.  The  rudimentary  milk 
molar,  which  is  absorbed  before  birth,  has  been  placed  over  the  third  or 
last  of  the  premolars,  which  succeeds  to  it  vertically. 

(“’)  Upper  and  lower  teeth  of  a  Dog,  which  are  placed  side  by  side  with 
those  of  the  Thylacine,  to  show  the  many  points  of  resemblance  between 
the  two  dentitions. 


472 


A  MANUAL  OF  DENTAL  ANATOMY. 


from  the  first  to  the  third,  but  the  last  true  molar  is  again 
a  smaller  tooth. 

The  upper  molars  are  all  of  the  “  carnassial  ”  pattern  ; 
there  is  a  “  blade  ”  elevated  into  subsidiary  cusps,  and 
internally  to  this  a  “  tubercle,”  supported  by  a  third  root. 

The  lower  molars  also  bear  some  resemblance  to  the  car¬ 
nassial  teeth  of  the  dog,  consisting  of  a  strong,  sharp-edged 
blade,  with  anterior  and  posterior  subsidiary  cusps,  the  latter 
being  somewhat  broad  and  tubercular. 

An  allied  animal  (Dasyurus  ursinus),  though  smaller  than 
the  Thylacine,  and  having  teeth  of  a  less  sectorial  character, 
is  so  destructive  to  sheep  and  so  fierce  and  untamable,  that 
it  has  earned  the  name  of  “  Tasmanian  Devil.” 

Within  the  limits  of  the  same  genus,  a  species  (Dasyurus 
viverrinus)  is  to  be  found,  in  which  the  molar  teeth  are 
studded  over  with  long  sharp  cusps,  like  the  teeth  of 
Insectivora,  a  group  which  it  resembles  both  in  its  habits 
and  food. 

A  number  of  smaller  marsupials  approximate  in  their 
dentition  more  or  less  to  the  Insectivorous  type,  whilst  a 
tolerably  complete  chain  of  existing  forms  serves  to  bridge 
over  the  gap  between  the  rapacious  Dasyuridse  and  the 
herbivorous  Kangaroos  and  Wombats. 


Amongst  the  Opossums  the  larger  species  have  large 
canines,  and  a  dentition  in  its  general  features  approxi¬ 
mating  to  the  Dasyuridse ;  they  feed  upon  birds  and  small 
mammals,  as  well  as  upon  reptiles  and  insects,  while  the 
smaller  species  are  more  purely  insectivorous. 

Myrmecobius,  a  small  Australian  marsupial  of  insectivo¬ 
rous  habits  and  dentition,  is  remarkable  as  having  teeth  in 
excess  of  the  number  of  the  typical  mammalian  dentition, 
having — 


m 


6 

6* 


In  the  Phalangers,  nocturnal  arboreal  animals  found  in 


THE  TEETH  OF  MA  BS  UP  I  A  LI  A . 


473 


Australia  and  a  part  of  the  Malay  Archipelago,  the  canines, 
though  present,  are  feeble  ;  an  interspace  also  separates  the 
incisors  from  the  molar  series. 

The  lower  incisors,  reduced  to  a  single  pair,  are  procum¬ 
bent,  and  grow  from  persistent  pulps ;  there  is  thus  func¬ 
tionally  some  faint  approach  to  the  character  of  a  rodent 

Fig.  208  (T). 


dentition,  as  may  be  seen  by  an  inspection  of  the  accom¬ 
panying  figure,  though  there  is  a  strongly  marked  transverse 
condyle  to  the  lower  jaw.  Phascolarctos  cinereus  has  been 
shown  by  Mr.  Oldfield  Thomas  to  have  the  same  reduced 
milk  dentition  as  Thylacinus. 

The  name  “  Kangaroo  Rats  ”  (Hypsiprymnus)  is  applied 
to  a  genus  consisting  of  about  a  dozen  species ;  they  are  all 
small  creatures,  not  much  larger  than  rabbits,  but  having 
the  general  proportions  of  Kangaroos.  They  are  quiet, 

f1)  Teeth  of  Phascolarctos  cinereus.  An  outline  figure  of  the  skull  is 
placed  above  to  show  the  general  “  rodent  ”  aspect  of  the  skull. 


474 


A  .MANUAL  OF  DENTAL  ANATOMY. 


gentle  little  creatures,  of  strictly  herbivorous  habits,  and 
they  are  interesting  to  the  odontologist  as  possessing  a 
dentition  which  throws  some  light  upon  several  anomalous 
extinct  forms,  whose  habits  and  affinities  have  been  the 
subject  of  much  controversy. 

The  dental  formula  is — ■ 


The  first  pair  of  upper  incisors  are  sharply  pointed,  are 
directed  nearly  vertically  downwards,  and  grow  from  per¬ 
sistent  pulps.  The  second  and  third  do  not  grow  from 
persistent  pulps,  and  their  worn  crowns  do  not  attain  to  the 
same  level  as  those  of  the  first  pair. 

All  three  pairs  are  antagonised  by  the  single  pair  of  large 
procumbent  lower  incisors,  of  which  the  sharp  points  meet 
the  first  pair  of  upper  incisors,  while  the  obliquely-worn 
surface  behind  the  cutting  edges  impinges  against  the  second 
and  third  upper  incisors. 

The  arrangement  of  the  incisors,  and  the  sharpness  of 
their  cutting  edges,  are  calculated  to  effect  the  same  objects 
as  those  attained  by  the  incisors  of  a  rodent ;  a  still  closer 
resemblance  would  be  brought  about  by  the  dwindling 
(which  occurs  in  other  genera)  and  final  disappearance  of 
the  second  and  third  upper  incisors,  and  a  compensating 
extra  development  of  the  first  pair. 

The  canines  are  not  large  ;  yet  they  are  not.  so  small  as 
to  be  termed  rudimentary ;  in  the  lower  jaw  they  are 
absent. 

Only  one  premolar  exists  in  the  adult,  and  this  is  a  very 
peculiar  tooth ;  its  crown  is  very  long  from  back  to  front 
(at  least  twice  as  long  as  any  of  the  molars,  and  in  some 
species  as  long  as  three  of  the  molars),  and  consists  of  a 
finely  furrowed  blade  with  a  sharp  edge ;  the  blades  of  the 
upper  and  lower  teeth  slide  over  one  another.  Behind  this 


THE  TEETH  OF  MARS UPIALIA. 


475 


there  are  four  true  molars,  with  square  quadricuspid  crowns, 
which  become  much  worn  down  by  use. 

The  last  and  only  premolar,  the  tooth  to  which  attention  has 
already  been  drawn  on  account  of  its  size  and  other  pecu¬ 
liarities,  by  virtue  of  its  great  size  displaces  not  only  the 

Fig.  209  (l). 


11V 


milk  molar,  to  which  it  is  the  legitimate  successor,  but  also 
turns  out  the  premolar  in  front  of  it,  a  tooth  belonging  to 
the  “  permanent  ”  series. 

In  this  particular  the  succession  of  the  teeth  in  the 
Hypsiprymnus  is  the  same  as  that  of  the  true  Kangaroo, 
which  may  be  understood  by  a  reference  to  Fig.  211. 

There  are  some  extinct  marsupials,  known  only  by  their 
jaws,  which  have  been  the  subject  of  much  controversy. 
Professor  Owen,  basing  his  arguments  largely  upon  the 
presence  of  premolars  which  possessed  elongated  and  sharp- 
edged  blades,  held  that  Plagiaulax  and  Thylacoleo  were 
carnivorous,  saying  of  the  latter  that  it  possessed  the  simplest 
and  most  effective  dental  machinery  for  predatory  life  known 

(*)  Upper  and  lower  teeth  of  Hypsiprymnus  (Bettongia)  (Grraii  ?) .  The 
dentition  represented  is  that  of  the  adult  animal,  the  permanent  premolar 
(pm3  in  the  figure,  pnq  if  we  accept  Mr.  Oldfield  Thomas’s  views — cf. 
p.  466)  being  already  in  place. 


476 


A  MANUAL  OF  DENTAL  ANATOMY. 


among  mammalia;  Dr.  Falconer,  in  the  case  of  the  first,  and 
Professor  Flower  in  the  case  of  the  Thylacoleo,  having  shown 
this  view  to  be  untenable,  or  at  least  unsupported  by  adequate 
evidence. 

Prof.  Marsh  has  described  several  Mesozoic  forms  like 
Plagiaulax,  but  upper  and  lower  jaws  not  having  been  found 
together  in  situ  it  is  somewhat  problematical  which  upper 
belongs  to  which  lower  jaw. 

The  lower  jaw  of  Ctenacodon,  found  in  strata  of  Jurassic 


Fig.  210  0). 


age,  has  a  single  long  pointed  incisor,  four  compressed 
cutting  premolars,  and  two  minute  tubercular  molars  behind 
them. 

The  clue  to  the  nature  of  the  great  blade-shaped  teeth  of 
these  extinct  creatures  is  afforded  by  the  form  of  the 
premolar  of  the  herbivorous  Hypsiprymnus  (see  Fig.  209). 
The  incisors  were  reduced  in  number,  and  were  large ;  the 
teeth  between  them  and  the  large  premolar  were  stunted ; 
but  both  these  points  are  true  of  the  herbivorous  Kangaroos. 
The  Thylacoleo  differs,  however,  from  all  known  animals  by 
the  immense  size  of  the  thin-edged  premolar  (worn  flat  in 
aged  animals),  and  by  the  rudimentary  condition  of  its  true 
molars.  But  its  incisors,  lying  forwards  and  closely  ap- 


0)  Lower  jaw  of  Ctenacodoa  (after  Marsh). 


THE  TEETH  OF  M A  RS  VP  I  A  LI  A . 


477 


proximated  in  the  middle  line,  are  particularly  unsuitable 
for  catching  and  holding  anything  alive  and  struggling, 
whilst  the  nearest  resemblance  to  the  blade-shaped  tooth  is 
to  be  found  in  harmless  herbivorous  creatures,  so  that  the 
balance  of  evidence  is  much  against  Professor  Owen’s  view. 

The  dental  formula  of  Thylacoleo  was — 


The  first  upper  incisor  was  very  large,  and  the  second  and 
third  very  small,  as  were  the  canine  and  the  first  two  upper 
premolars :  but  the  last  upper  and  the  only  lower  premolars 
were  great  blade  shaped  teeth  like  the  large  premolar  of 
Hypsiprymnus,  only  far  larger. 

Thus  its  useful  teeth  were  only  a  pair  of  incisors  above 
and  below,  and  a  pair  of  sectorial  premolars. 

The  Kangaroos,  comprising  many  species  of  very  varying 
size,  are  all  docile  creatures  (with  the  exception  of  a  few  old 
males),  of  herbivorous  habits ;  they  in  some  particulars 
recall  the  ruminants. 

Their  dental  formula  is — 

.301  4 

l  -  c  -  p  -  m 

1  0  1  1  4 

The  three  pairs  of  upper  incisors  are  more  equal  in  size  than 
in  the  Hypsiprymnus,  and  the  central  pair  do  not  grow  from 
persistent  pulps.  The  lower  incisors  are  very  peculiar 
teeth  :  they  grow  from  persistent  pulps,  are  procumbent, 
projecting  forwards  almost  horizontally,  and  are  very  much 
flattened  from  side  to  side,  their  outer  surfaces  being  but 
slightly  convex,  and  their  inner  surfaces  flat,  with  a  median 
ridge.  Their  margins  are  almost  sharp.  There  is  an  un¬ 
usual  amount  of  mobility  between  the  two  halves  of  the 
lower  jaw,  so  that  these  two  teeth  can  be  to  a  slight  extent 
separated  from  one  another. 

The  upper  canine  is  often  present  as  a  very  minute 


478  A  MANUAL  OF  DENTAL  ANATOMY. 


rudiment,  but  in  no  Kangaroo  does  it  attain  to  a  greater 
size. 

The  dentition  of  the  Kangaroo  is  somewhat  perplexing 
to  the  student,  for  two  reasons  :  the  one,  that  the  last  or 
third  permanent  premolar  not  only  displaces  the  solitary 
milk  molar,  but  also,  as  in  Hypsiprymnus,  on  account  of  its 


Fig.  211  (b). 


greater  size,  the  second  permanent  premolar,  which  was  in 
front  of  the  milk  molar ;  and,  besides  this,  in  animals  past 
adult  age,  teeth  are  shed  off  from  the  front  of  the  molar 
series  till  at  last  only  the  last  two  true  molars  on  each  side 
remain. 

Thus  the  dentition  of  the  Kangaroo  at  successive  ages  may 

be  thus  represented — 

.301,1  4 

l  -  c  —  p  -  dm  -  m 

1  0  1  1  1  4 

or,  in  all,  six  molar  teeth.  Then  the  third  premolar  displaces 

0)  Upper  and  lov/er  teeth  of  Halmaturus  ualabatus.  The  permanent 
premolar  is  not  yet  erupted,  and  is  shown  in  its  crypt :  when  it  comes 
into  its  place  it  will  displace  the  milk  molar,  and  one  of  the  anterior  pre¬ 
molars  as  well.  In  the  upper  jaw  a  rudimentary  canine  is  shown.  The 
point  of  the  lower  incisor  would  fit,  in  closure  of  the  mouth,  behind  the 
long  anterior  upper  incisor,  but  the  width  of  the  page  did  not  admit  of  the 
teeth  being  placed  in  their  true  relative  positions  without  reduction  in 


size. 


THE  TEETH  OF  MARS  UPIA  LI  A . 


479 


the  second  true  permanent  premolar  as  well  as  the  milk 
molar,  and  we  have— 

.301,  N  4 

i  -  c  —  p  -  (a  new  one)  m 

1  0  1  1  V  '  4 

or,  in  all,  only  five  molar  teeth. 

Then,  one  after  another,  teeth  are  shed  off  from  the  front 
of  the  molar  series,  just  as  in  the  Phacochserus  (see  page 
406),  till  all  that  is  left  is — 

3  0  0  2 

i  -  c  -  p  -  m 
1  0*0  2 

The  milk  molar  of  the  Kangaroo  is  a  fully-developed  tooth, 
which  takes  its  place  with  the  other  teeth,  and  is  not  dis¬ 
tinguished  from  them  by  any  special  characters,  so  that  mere 
inspection  of  the  jaw  of  a  young  Kangaroo  having  it  in  place, 
at  the  same  time  with  a  premolar  in  front  of  it  and  four  true 
molars  behind  it,  would  not  lead  an  observer  to  suspect  its 
real  nature. 

No  existing  creature  serves  to  connect  the  Kangaroos 
closely  with  the  Wombat,  but  the  extinct  Diprotodon  appears 
to  have  in  a  measure  bridged  across  the  gap. 

The  Wombats  (Phascolomys)  are  heavily-built,  inoffensive 
creatures,  which  burrow  in  the  ground  and  subsist  largely 
upon  roots.  In  their  dentition  they  closely  simulate  the 
rodents,  as  they  possess  but  a  single  pair  of  chisel- edged 
incisors  in  either  jaw,  growing  from  persistent  pulps,  and 
embedded  in  very  deep  and  curved  sockets.  These  differ 
from  the  corresponding  “  dentes  scalprarii  ”  of  true  rodents 
in  that  there  is  a  complete  investment  of  cement,  which 
passes  over  the  enamel  in  front  of  the  tooth  as  well  as  cover¬ 
ing  its  back  and  sides.  They  are  unlike  the  teeth  of  other 
marsupials  in  their  structure,  as  the  dentinal  tubes  do  not 
penetrate  the  enamel,  which  is  therefore,  probably,  harder 
and  denser  and  so  less  readily  worn  away. 


480 


A  MANUAL  OF  DENTAL  ANATOMY. 


Ihe  molar  teeth  also  grow  from  persistent  pulps,  and  are 

very  deeply  grooved  upon  their  sides,  so  that  their  grinding 
surfaces  are  uneven. 

Their  dental  formula  is — 


The  first  tooth  of  the  molar  series  is  a  single  column 


Fig.  212  (J). 


~§~  Nat.  Size. 


whereas  the  deep  grooving  of  the  others  divides  them  into 
two  columns,  so  that  its  simpler  appearance,  as  well  as 
analogy,  would  indicate  that  it  is  a  premolar.  But  no 
succession  whatever  has  been  observed  in  the  Wombats. 

The  adaptive  resemblance  to  the  dentition  of  the  true 
rodents  is  exceedingly  close,  though  the  Wombat  is  an 
undoubted  marsupial ;  and  the  very  closeness  of  the  imita¬ 
tion  is  an  exemplification  of  the  fact  that  adaptive  charac¬ 
ters  are  very  apt  to  mislead,  if  used  for  the  purposes  of 
classification. 

Extinct  Wombats,  of  very  much  larger  size  than  the 
(b  Upper  and  lower  teeth  of  Wombat  (Phascolomys  wombat). 


THE  TEETH  OF  MA  RS  U PI  A  LI  A . 


481 


recent  species,  are  found  in  the  later  tertiary  deposits  of 
Australia. 

Amongst  the  marsupials  there  is  a  pretty  little  arboreal 
creature  (Tarsipes),  not  larger  than  a  small  rat,  which  sub¬ 
sists  upon  insects  and  the  nectar  of  flowers,  which  it  reaches 
by  means  of  a  long  protrusibie  tongue.  Its  molar  teeth 
are  rudimentary,  variable  in  number,  and  are  soon  shed  ; 
the  lower  incisors,  which  are  procumbent,  are  however  re¬ 
tained,  as  are  a  few  small  teeth  which  are  opposed  to  them 
above. 

The  wonderful  diversity  of  the  forms  into  which  the 
marsupials  have  branched  out  in  Australia  seems  to  prove 
that  they  have  been  established  in  that  region,  and  have 
been  without  the  competition  of  more  highly  organised 
placental  mammals,  for  a  prodigious  length  of  time ;  and 
one  cannot  better  conclude  the  very  brief  survey  of  the 
teeth  of  mammalia  which  has  been  attempted  in  this  volume 
than  by  calling  the  reader’s  attention  again  to  the  character 
of  the  marsupial  fauna — this  microcosm,  in  which  every 
place  is  filled  by  a  marsupial  which  mimics  the  placental 
mammal  which  it  represents — for  nowhere  can  we  more 
plainly  see  the  workings  of  natural  selection  than  in  areas 
thus  isolated  and  deprived  of  immigrant  creatures  for  count¬ 
less  ages. 

In  the  foregoing  pages  much  stress  has  been  laid  upon 
the  variability  of  animals,  and  the  agencies  by  means  of 
which  the  variations  have  been  preserved  and  intensified, 
so  to  speak,  so  that  ultimately  permanent  hereditary  modi¬ 
fications  have  been  the  result,  variations  be  it  noted  not 
always  small  (see  p.  294) ;  and  it  is  possible  that  in  laying 
this  aspect  of  the  matter  prominently  before  the  reader 
an  impression  of  too  great  instability  may  have  been  con¬ 
veyed  ;  and  thus  the  teeth  of  creatures  made  to  appear 
more  plastic  and  more  shifting  than  they  really  are,  for  it 
is  hardly  possible  to  realize  the  enormous  lengths  of  time 


482 


A  MANUAL  OF  DENTAL  ANATOMY. 


during  which  the  agencies  have  been  at  work,  and  without 
which  they  would  have  been  powerless  to  produce  profound 
alterations. 

The  process  which  we  term  inheritance  is  constantly  re¬ 
producing  animals  which  are  minute  copies  of  their  parents ; 
copies  which  are  even  more  exact  than  we  can  at  first  sight 
realise. 

Thus,  even  amongst  different  species  of  the  same  genus, 
whose  teeth  are  apparently  quite  similar  so  far  as  their 
number  and  pattern  goes,  differences  exist  which  are  constant 
for  the  species,  and  which  may  be  brought  into  promi¬ 
nence  by  any  method  of  investigation  which  is  sufficiently 
accurate.  And  those  engaged  in  the  practice  of  dental 
surgery  meet  with  curious  examples  of  inherited  variation, 
sometimes  taking  the  form  of  irregularity  in  the  position  of 
teeth,  and  sometimes  of  the  absence  or  dwarfing  of  a 
particular  tooth  ;  these  abnormalities,  running  through 
several  generations,  are  often  presented  by  a  large  pro¬ 
portion  of  the  children  of  one  generation. 

Nature  is  never  extravagant,  and  an  organ  which  owing 
to  altering  conditions  is  becoming  superfluous,  is  sure  to  be 
destroyed.  For  the  operation  of  natural  selection  is  just  as 
necessary  for  the  preservation  of  an  organ  which  has  arrived 
at  a  certain  standard  by  the  process  of  evolution  as  it  was 
for  the  bringing  it  up  to  that  standard — the  remission  of  the 
operations  of  natural  selection  lead  surely  to  its  degradation 
and  final  disappearance. 

And  so  it  happens  that  whilst  an  organism  is  as  a  whole 
progressing,  some  of  its  parts  may  be  becoming  superfluous, 
and  be  retrograding,  after  a  time  coming  down  to  the  con¬ 
dition  of  rudimentary  organs.  Thus  almost  all  early  mam¬ 
malia  had  a  continuous  row  of  teeth,  with  no  diastema;  from 
this  the  teeth  of  monkeys  had  advanced  in  specialisation  and 
acquired  a  diastema,  but  in  man  the  diastema  has  been  lost 
again,  so  that  qua  the  teeth,  man  has  retrograded. 


THE  TEETH  OF  MARS  TJ PI  ALIA . 


483 


It  is  perhaps  disappointing  that,  comparatively  simple, 
accessible  and  indestructible  as  teeth  are,  no  satisfactory 
comprehensive  scheme  of  their  evolution  even  in  mammalia 
has  been  set  forth.  The  extreme  imperfection  of  the 
geological  record  is  such  that,  with  the  exception  of  a  few 
comparatively  small  groups,  the  material  upon  which  to 
build  wide  generalisations  is  not  to  hand,  and  too  many 
gaps  remain  to  be  bridged  over  by  conjecture. 

Professor  Cope,  who  is  an  advocate  of  the  mechanical 
genesis  of  tooth  forms,  has  been  the  chief  worker  in  this 
field  (Homologies  and  origin  of  types  of  molar  teeth, 
Journ.  Philadelph.  Acad.  1874,  and  numerous  papers  in 
American  Naturalist),  and  he  holds  that  the  primitive 
mammalian  tooth  must  have  been  a  simple  cone,  like  a 
cetacean  tooth  (“  Haplodont  ”),  and  that  this  was  first 
complicated  by  the  addition  of  low  cusps  before  and  behind, 
and  subsequently  also  laterally. 

These  early  teeth  would  have  alternated  with  one  another 
in  closure  of  the  jaws,  and  this  alternation  of  the  teeth  lasted 
for  a  long  period  in  geologic  time. 

It  has  been  pretty  well  established  by  Professor  Cope  and 
Professor  Osborn  (p.  318)  that  Mesozoic  mammals  had 
attained  the  stage  in  which  the  molars  were  trituberculate, 
but  the  teeth  still  interdigitated,  and  did  not  meet  grinding 
surface  to  grinding  surface. 

But  although  Professor  Cope’s  researches  have  been  of  the 
utmost  value,  and  some  of  his  terms  have  obtained  general 
currency,  fresh  facts  are  continually  coming  to  light,  which 
render  attempts  at  absolute  generalisation  almost  futile.  As 
an  example  we  may  take  the  recently  discovered  teeth  of 
Ornithorhyncus.  Now  this  is  a  mammal  of  so  low  a  type, 
and  with  so  many  affinities  with  the  Sauropsida  that  we 
might  have  fairly  expected  that,  if  it  had  teeth  at  all,  they 
would  have  been  of  the  simplest  conical  form.  But  instead 
of  their  being  such,  they  are  of  complex  form,  and  show 

i  i  2 


484 


A  MANUAL  OF  DENTAL  ANATOMY. 


indications  of  descent  from  some  creature  in  which  they 
were  more  complete,  and  functionally  more  active. 

So  this  discovery,  instead  of  helping  us  much  in  our 
speculations,  seems  to  relegate  to  a  still  more  remote  period 
that  common  ancestor  whose  teeth  were  all  simple  cones, 
if  such  there  were ;  but  there  remains  an  ample  scope  for 
work  of  this  kind  in  the  study  of  the  homologies  of  the 
teeth  of  those  ancient  animals  which  are  already  known, 
whose  numbers  are  being  added  to  almost  every  day. 


INDEX 


PAGE 

Aardwolf,  teetli  of  429 

Absorption  of  teeth  .  200,  202 

Acrodont,  meaning  of  term  .  .  258 

Acrodus,  teeth  of  237 

Adaptive  modification,  meaning 

of  term . 290 

Albrecht,  on  intermaxillary  bone 

9,  187 

Alveolar  process  .  .  .  .  26 

,,  ,,  development  of, 

188,  210 

Alveoli,  attachment  by  means  of.  192 
Alveolo- dental  membrane.  115,  226 

Amblypoda . 415 

Ameloblast  cells  .  .  .  .  162 

Amphitherium  .  .  .  .312 

Amphioxus . 227 

Anarrhicas,  teeth  of  .  .  .  247 

Anchippodon . 420 

Anchylosis  of  teeth  .  .  .  219 

Angler,  teeth  of  .  .  214,  245 

Anoplotherium,  teeth  of  .  .  400 

Anteaters,  teeth  of  .  .  .  .  333 

Anthropoid  apes,  teeth  of  .  .  449 

,,  order  of  eruption  of  .  451 
,,  teeth  in  comparison 

with  man  .  .451 

Antrum . 29 

„  teeth  in  relation  with  .  31 
Archetype  theory  .  .  .  304 

Archaeopteryx,  teeth  of  .  .  .279 

Arctoidea  ....  421,  433 

Armadillo,  teeth  of  .  8,  46,  326,  334 
Articular  process,  share  of  in 
growth  of  jaw  .  .  .  .  192 

Articulation  of  the  lower  jaw  .  34 

,,  ,,  teeth  with  one 

another  .  .  .  5 

Artiodactyle  ungulata  .  402,  414 

Ateles . 447 

Attachment  of  teeth  .  .  .213 


PAGE 

Attachment  of  teeth  by  membrane  213 

by  hinges  .  214 
by  anchy¬ 
losis  .  .  219 

by  sockets  .  225 

bone  of  .  .  220 

Aye-aye,  teeth  of  .  .  298,  443 

milk  teeth  of  .  .  .  444 


B. 


99 

99 


99 

99 


99 

99 


99 


Babirussa,  teeth  of 
Baboon,  teeth  of 
Balsenidae,  whalebone  of 
Barracuda  pike,  teeth  of. 
Basal  ridge,  or  cingulum. 
Basement  membrane  of 


.  291,  407 
305,  447 
.  .  342 
.  253 
.  .  11 
tooth 

germ . 182 

Bathysaurus  ferox,  teeth  of.  .  218 

Batrachia . 231 

Bats,  teeth  of  ...  357 

,,  milk  teeth  of  .  .  359 

Bdellostoma,  teeth  of  .  .  .  228 

Bear,  teeth  of .  .  .  423,  435 

Beard,  Dr.,  on  horny  teeth  228,  257 
Beaver,  teeth  of  .  .  .51 

Bettongia,  teeth  of .  .  .  .  475 

Bicuspids,  human  .  .  .15 

Bilophiodont,  meaning  of  term 

389,  390 

Binturong  ...  .  .  427 

Birds,  teeth  of  .  .  .278 

Boar,  tusks  of . 404 

Bodecker,  on  enamel  structure  .  52 

„  on  dentine  .  .  .  74 

Boll,  on  dentinal  fibrils  .  .  77 

Bone  of  attachment.  .  .  .  220 

primary  .  .  .  177,  181 

zb.  ib. 

.  227 
399,  419 


9  9 

,,  development  of 
Branchiostoma  . 
Brontotheridoe . 


486 


INDEX. 


PAGE  I 

Brooke,  Sir  Victor,  on  canines  of 
Cervidae  .  .  .  .  .  412 

Brown  striae  of  Ketzius  .  58,  66 

Buccinator,  attachment  of  .  .  32 

Bunodont,  meaning  of  term  324,  400, 

405 

Bunotkeria . 420 


C. 


Calcification,  dates  of  in  the  seve- 


ral  teeth  . 

.  191 

process  of  . 

.  157 

1  •> 

of  enamel 

.  160 

5  J 

of  dentine 

.  168 

of  vaso-dentine 

.  174 

5? 

of  osteo-dentine 

.  176 

of  cementum  . 

.  177 

Calcified 

teeth 

3,  45 

Calcoglobulin  .... 

.  159 

Calcospherites 

.  159 

Camel,  teeth  of 

.  409 

Canaliculi  of  cementum 

.  106 

Canidao, 

teeth  of 

.  426 

Canine  teeth  of  ruminants  . 

.  309 

5  1 

of  lemurs  . 

.  310 

of  oreodon 

.  ib. 

of  mole 

.  ib. 

?> 

of  inseetivora  . 

.  ib. 

Canine,  definition  of  .  .  .  307 

,,  sexual  development  of  .  299 
„  true  signification  of  term.  308 
Canines,  human  .  .  .  .14 

Capybara,  teeth  of  .  .  296,  367 

, ,  molar  teeth  of  .  .  364 

Cai’charias,  teeth  of  .  .  .  235 

Carnassial  tooth  ....  423 
Carnivora,  milk  dentition  of  .  .  424 

„  teeth  of  421 

Carnivorous  dentition,  general 

character  of . 424 

Castor . 368 

Catarrhine  monkeys,  teeth  of  .  .  447 

Cebus . 451 

Cement  organ . 153 

„  doubtful  existence  .  156 
Cement,  over  crown  of  tooth  .  .  105 

Cement  um . 104 

rudimentary  .  .  .105 

structure  of  .  .  ib. 

distribution  of  .  .  47 

calcification  of  .  .  177 

Ceratodus,  teeth  of  ...  240 

Cervulus . 413 

Cestracion,  teeth  of  .  220,  236 

Cetacea,  teeth  of  .  .  .  .  336 


>> 

n 


TAGE 


449, 

349, 


Cingulum, 


Cetacea,  teeth  of,  dentine  of 
Chsetodonts,  teeth  of  . 
Chauliodus 

Cheiromys,  milk  teeth  of 
,,  teeth  of 
Chelonia,  teeth  of 
Chimpanzee  . 

Chiroptera,  teeth  of 
Chrysochloris  . 

definition  of 
developed  into 
tional  cusps 

Coatimundi,  teeth  of  . 

Cobra, teeth  of 
Complex  teeth,  manner  of 
ation  of  . 

Contour  lines  of  Owen 
Cope,  Prof.,  views  of  . 

Coronoid  process,  use  of  in  growth 
Correlations  of  growth  .  .  . 

Craspedocephalus 
Crocodiles,  teeth  of  .  .  .  . 

implantation  of  teeth 


.  66 
241 
277 
297 
296 
258 
451 
357 
320 
.  11 
addi- 
.  .  318 
.  434 
266,  272 
form- 

.  316 
.  .  66 
483 
199 
300 
267 
275 


289, 


>» 


of  .  .  .  .226 

,,  succession  of  teeth  in  .  275 
Crypts  of  developing  teeth  .  .189 

Ctenacodon  .  .  .  466,  476 

Curvatures  of  dentinal  tubes  .  .  65 
Cusps,  formation  of  320 

Cuticula  dentis  .  .  .  .  109 

Cyclostomata  ....  227 

Cynodi’aco . 277 

Cynoidea . 424 

Cystophora,  teeth  of  .  .  439 

Czermak,  interglobular  spaces  of  .  80 


D. 

Dasyurus,  teeth  of.  314,  328,  466,  472 
Deciduous  dentition  .  .  .  326 

Decussation  of  enamel  prisms  .  .  50 

Deer,  teeth  of  .  .  .410 

canine  teeth  of  .  .  299,  412 

Deficiencies  of  teeth  in  hairy  men  301 
,,  „  in  Turkish 

dogs  .  .  301 

Dentine,  calcification  of  .  .  168 

,,  „  osteo  .  .  176 

,,  „  yaseo- den¬ 
tine.  .  174 

„  composition  of  .  .  .  62 

,,  fibrils  .  .  .  .70 

„  „  •  hleumann  on  74 

,,  germ . 138 

,,  globular  .  .  .173 

,,  granular  layer  of  .  .  78 


INDEX. 


487 


PAGE 


Dentine,  interglobular  spaces  of  .  78 

„  matrix  of  .  .62 

„  modifications  of,  in  laby  • 

rinthodon  85 
„  ,,  in  lepidosteus  84 

„  „  in  manatee  89,  92 


in  megathe- 


V 


V 

n 


94,  98 
82,  97 


>5 


num  90 
„  in  myliobates 

83,  87 

„  in  varanus  .  82 

osteo- 

plici-  ... 

„  secondary  .  .  .  .  98 

,,  sensitiveness  of  .  .77 

,,  sheaths  of  Neumann  in  .  68 

,,  termination  of  tubes  of  .  78 

„  theories  as  toformation  of  170 

,,  tubes  ...  58,  64 

,,  un vascular  .  62,  97 

„  varieties  of  .  .  .97 

,,  vascular  .  .  .  .  89 

vaso-  ...  88, 98 

formative  cells  of  .  .169 

Dentition,  t}rpical  mammalian  .  304 
Dents  en  velours,  en  brosse,  en 

cardes . 241 

Dermal  spines  of  fish  .  2,  127,  235 

Desmodus,  teeth  of  .  .  357,  359 

Development  of  the  teeth  121  ct  seq. 

,,  commencement  of  .  121 

,,  in  eel  ...  129 

„  in  fishes  .  .  .  123 

,,  in  lizards  .  .  .  133 

,,  in  mammalia  .  .136 

„  in  reptiles  .  .  .130 

„  in  snakes  .  .  133 

,,  of  the  true  molars  146 

„  of  the  jaws  .  .186 

, ,  of  the  alveolar  pro¬ 
cesses  .  188,  201 

Diastema . 398 

Dicynodon,  teeth  of  .  .  .  261 

Didelphys . 466 

Dinoceras,  teeth  of  .  .  .  416 

Dinosauria,  teeth  of  .  .  276 

Dinotherium,  teeth  of .  .  .  382 

Diodon,  teeth  of  .  .  .  247 

Diphyodont,  meaning  of  term  .  326 
Diprotodon,  teeth  of  .  .  466,  479 

Dog,  teeth  of  ...  424 

„  variation  in  teeth  of  .  .  427 

Dog-fish,  teeth  of  .  2,  123,  127,  231 
Dolphin,  teeth  of  336 

Dryptodon,  teeth  of  .  .  .  420 

Dugong,  teeth  of .  .  .  .  345 

„  tusks  of  male  .  .  .  345 


E. 

PAGE 

Echidna  .  .  .  .  .  .  289 

Edentata,  teeth  of  333 

Eel,  deA-elopment  of  teeth  of  .  .129 

,,  enamel-tipped  teeth  of  45, 

129,  223 

Elaehistodon  ....  264 
Elaphodus  ...  .  .  299 

Elasmobraneli  fish,  teeth  of  .123 
Elephant,  milk  teeth  of  .  .  .  372 

„  molars  of  .  .  371,  377 

,  succession  of  teeth  in  .  377 
„  structure  of  teeth  of  .  386 
,,  tusks  of  .  .  .371 

Enamel  .  .  48  et  seq. 

,,  absence  of  .  .46 

„  cavities  in  .  .  .  58 

calcification  of  .  .  160 

cells . 161 

„  calcification  of  .163 
entry  of  dentinal  tubes  into  58 
fracture  of  .  .57 

germ  .  .  .  122,  134 

of  Sargus  .  .  .60 

of  marsupials  .  .  .  53 

organ,  development  of 

119,  122,  142 
„  external  epithe¬ 

lium  of  140,  142,  144 
„  internal  epithe¬ 

lium  of  140,  142,  162 
,,  neck  of  .  .  132,  140 

pigment  in  .  .  .  58 

prisms  of  .  .  49,  369 

rudimentary  .  .  .  46 

organ,  stellate  reticulum 

of  139,  140,  166 

,,  striation  of  .58 

,,  vascularity  of  .  .  144 

theories  of  formation  of  .  160 

tubular  .  .  .  .54 

.  .  388 

.  393 

Erinaceus  .  .  .  .  .  351 

Eruption  of  teeth,  date  of  .  .  201 

Esthonyx . 421 

External  pterygoid  muscle,  action 
of . 36 


V 


Eocene  mammalia 
Eohippus 


F. 

Felidae,  teeth  of  . 
Fibrils  of  dentine  . 
Fishes,  teeth  of  . 

,,  classification  of 


421,  430 
.  .  70 
.  227 
.  .  ib. 


488 


INDEX. 


PAGE 

Fishes,  structure  of  teeth  of  .  .  254 

Flounder,  teeth  of  .  .  .91 

Flower,  Prof.  326,  335,  393,  462,  467, 

et  passim 

Foetus  (nine  months),  teeth  of  .  190 
Follicle,  dental  .  .  .  141,  151 

Frog,  teeth  of  132,  256 


G. 

Galeopithecus,  teeth  of  .  .  .  350 

Galesaurus . 275 

Ganoid  fish  .  .  .83,  129,  240 

Gegenbaur,  Prof.  .  128,  et  passim 
Germ,  tooth  ....  121 

Gibbon . 449 

Glenoid  cavity,  form  of  in  car¬ 
nivora  38 

,,  „  form  of  in  her- 

bivora  39 

Globular  dentine  .  .  .  .173 

Glyptodon . 336 

Goodsir,  special  views  of  .  .  150 

Gorilla  ....  449,  455 

Grampus,  teeth  of  .  .  .  .  337 

Granular  layer  of  dentine  .  .78 

Growth  of  the  jaws.  .  .  .  186 

Gubernaculum  ....  156 

Gum,  the . 114 

Gunther,  Dr.  .  .  261,  et  passim 

Gymnodonts,  teeth  of  .  .  247 


H. 

Haddock,  teeth  of  223 

Hair  and  teeth,  correlation  be¬ 
tween  .  301 

Hairless  dogs,  teeth  of  .  .  ib. 

Hairy  men . ib. 

Hake,  dentine  of.  .  93,  98,  214,  245 

,,  hinged  teeth  of  .  .  214 

Halicore . 345 

Falmaturus,  teeth  of  .  468,478 

Haplodont  ....  483 
Hare,  teeth  of.  .  .  51,  362 

Hatteria,  teeth  of  .  .  256,  261 

Hedgehog,  teeth  of .  .  .  .  351 

Heloderma,  teeth  of  .  .  .  259 

Hesperornis,  teeth  of  .  .  279 

Heterodont,  definition  of  .  .  326 

Hinged  teeth  ...  .  .  214 

Hipparion,  teeth  of  .  393,  396,  398 

Hippocampus . 252 

Hippopotamus,  teeth  of  .  .  408 

Homalodontotherium  .  .  10,  313 


PAGE 

Homodonts,  definition  of  term  .  325 
Homologies  of  the  teeth  .  .  304 

Horny  teeth  .  .  .  .  .  4 

,,  ,,  structure  and  de¬ 
velopment  of  .  .  228 

Horse,  teeth  of  .  .  .  .  395 

,,  incisor  tooth  of  .  .  .  316 

,,  ancestry  of  .  393 

Human  teeth,  forms  of  .  .  .  458 

Huxley,  Prof.,  special  views  on 

development .  151 
,,  ,,  on  enamel  develop¬ 

ment  161,  286,  et  passim 
Hysena,  teeth  of  .  .  .  428 

Hysenodon,  teeth  of  .  .  .  433 

Hydromys,  teeth  of .  .  360,  364 

Hydrophis,  teeth  of  .  .  265,  268 

Hydropotes,  canines  of  .  299,  412 

Hyperoodon,  teeth  of  .  .  .  338 

Hypsipiynmus,  teeth  of  329,  467,  477 
Hypsodont,  meaning  of  .  .  .  400 

Hyracodon  .....  399 
Hyrax,  teeth  of  .  .  .  369 

Hystrix . 369 

I. 


|  Ichthyornis,  teeth  of  .  .  .  279 

1  Ichthyosaurus  .  .  .  .  276 

Iguanodon,  teeth  of  .  .  260,  276 

Incisors,  definition  of  .  .  306 

„  human,  description  of  .  10 

Insec tiv ora,  teeth  of  .  .  .  349 

,,  characteristic  molars 

of.  ib. 

Interglobular  spaces  .  .  .78 

Intermaxillary  bones  .  .  9,  187 

Internal  pterygoid  muscle  .  .  36 


J. 

Jaws,  development  of  .  .  .  186 


K. 

Kangaroos,  teeth  of  .  .  469,  478 

Kangaroo,  enamel  of  .  .  .  59 

,,  dentine  of  .  .  .  ib. 

Kelt,  sexual  development  of  jaws 

in  .....  254 


L. 


Labyrinthodon,  teeth  of . 
„  ,,  dentine  of 


.  257 
.  85 


INDEX. 


489 


» 

5> 


PAGE 

Lacunae  of  cementum  .  .  .  106 

development  of  .  108,  180 

encapsuled  .  107,  180, 415 

„  in  pits  of  enamel  .  .112 

„  of  Howship  .  200,  208 

Lamna,  teeth  of  .  .  .  .  232 

„  dentine  of  .  .  .  .  96 

Lamprey,  dental  tissues  of  .  .43 


teeth  of 

Lankester,  Prof.  Ray 
Lemurs,  teeth  of 
,,  canines  of 
Lepidosiren,  teeth  of  . 

Lepidosteus,  dentine  of 
Leporidae 
Leptocardii 
Leptothrix ,  in  interglobular  spaces  80 
Lines  of  Schreger  .  .  .66 

133,  258 
.  245 
.  .  325 

.  68 


.  .  228 
307,  339,  341 
.  296,  442 
.  .  310 
.  240 
83,  240 
.  51,  362 
.  .  227 


Lizards,  teeth  of 


Lophius,  teeth  of. 
Lophodont,  meaning  of  term 
Lumen,  appearance  of. 


M. 

Macaque  monkey 
Machairodus,  teeth  of 
Mackerel,  teeth  of 
M  acropus,  teeth  of  . 
Macroscelis  . 

Malar  process 
Mammalia,  teeth  of 


447 

431 

225 

466 

319 


yy 


.  .  26 
136,  283,  et  seq. 
,,  typical  dentition  of  .  304 

,,  teeth  of,  early  .  318,  482 

Mammoth,  tusks  of  .  373 

Man,  teeth  of  .  .  .1,  458,  459  i 

teeth  of  different  races  of  .  460 

.  347 
89,  347 
50,  348 
.  31 
.  333 
.  395 
.  464 
.  467 
of 

53,  468 
.  32,  35 
37 

322,  380,  386 
.  .  381 

.  381 
.  .  26 


Manatee,  teeth  of 
,,  dentine  of 
,,  enamel  of  . 

Mandible  .... 
Manis  .  .  -  . 

Mark  of  horses’  incisors 
Marsupialia,  teeth  of 

milk  teeth  of  . 
peculiar  enamel 


yy 


Masseter  muscle 
Mastication,  muscles  of 
Mastodon,  teeth  of 
,,  molars  of 

,,  milk  teeth  of 

Maxillte,  description  of 

development  of  growth  of  186 
V-shaped  .  .  .  212 

Meckel’s  cartilage  .  .  .  .  186 


yy 

yy 


Megaderma 

Megatherium,  dentine  of 
Melursus,  teeth  of  . 
Membrana  eboris  . 

„  preform ativa  . 
Mental  foramen,  position  of 
Merganser,  bill  of  . 
Mesohippus .... 
Mesonyx 
Mesoplodon. 

Microlestes 

Milk  dentition,  character  of 
rudimentary 


yy 


origin  of 


Miohippus 
Molars,  definition  of  . 
Mole,  teeth  of 
„  milk  teeth  of 
Molossus .... 
Monkeys,  teeth  of 

„  premolars  of 
Monodon,  teeth  of 
Monophyodont,  definition  of 
Monotremata,  teeth  of  . 
Moseley,  Prof.  .  .  307, 

Muridae,  enamel  of 
Muscles  of  mastication 
Musk  deer,  canines  of 
„  teeth  of 
Mustelidae,  teeth  of 
Mutica.  .  .  .  . 

Mycetes 

Myliobates,  dentine  of 
„  teeth  of 
Myrmecobius,  teeth  of . 
Myslicoceti 
Myxine,  teeth  of 

X. 


PAGE 

.  359 
.  90,  334 
.  .  436 

149,  168 
113,  181 
.  194 
.  278 
.  393 
.  349 
.  339 
.  289 
.  325 
.  328 
.  332 
.  398 
20,  306 
.  354 
.  356 
.  359 
.  446 
.  16,447 
.  341 
.  325 
.  .  286 
et  passim 
.  .  368 
.  37 
.  .  299 
299,  412 
.  .  433 

.  333 
.  .  447 
83,  87 
.  .  238 
.  472 
.  .  336 
44,  227 


Narwal  .  .  .  .  291,  341 

,,  teeth  of  .  .  .  .  ib. 

Nasal  process  .  .  .  .26 

Nasmyth’s  membrane,  nature  of  .  109 
Neck  of  enamel  organ  .  .  132,  140 


yy 


of  tooth 
Nerves  of  dentine 
„  of  the  pulp  . 

,,  of  the  teeth 
Neumann,  sheaths  of 
Newt,  teeth  of 

O. 


7 

.  77 
.  75,  102 
.  40 
.  .  68 
132,  257 


Oblique  ridge  of  human  molars  .  20 

Odontoblast  cells  .  .  72,  101,  168 


490 


INDEX. 


PAGE 

Odontoceti.  .  .  .  .  336 

Odontoptei-yx,  teeth  of  .  .  278 

Odontornithes,  teeth  .  .  .279 

Odontostomus,  hinged  teeth  of  .  219 

(Eluroidea . 421 

(Etobatis . 239 

Ophidia,  development  of  teeth  of 

133,  261 

Opossum,  teeth  of  472 

Orang,  teeth  of  .  .  18,  449,  451 

Oreodon,  teeth  of  309 

„  canines  of .  .  .  .  310 

Ornithorhyncus,  teeth  of  .  3,  8,  230, 

284,  483 

Orohippus  .....  393 
Orycteropus,  dentine  of  .'  .  88,  335 
Osborne,  Prof.  H.  F.,  on  Mesozoic 

mammals . 318 

Osseous  fish,  teeth  of  .  .  241 

„  development  of  teeth 

of  128 

Osteoblasts  .  .  .  176,  178 

Osteoclasts  • .  .  .  .  .  208 

Osteodentine  .  .  .  .  .  94 

,,  in  teeth  of  rodents  .  366 
„  in  teeth  of  sperm 

whales  .  .  98,  316 

Ostracion,  dentine  of  .  .  .93 

Otaria,  erosion  of  teeth  of  .  .  437 

,,  teeth  of  .  .  .  ib. 

Otocyon,  dentition  of  .  .  426 


P. 

Palaeichthyes,  teeth  of  .  .  .  230 

Pantotheria . 312 

Papilla,  formative  .  145,  et  passim 

Paradoxurus  .....  427 

Parrot  fish,  teeth  of  .  .  249 

Pecora  ......  409 

Perameles  .....  466 

Perch,  teeth  of  .  .  .  167 

Periosteum,  alveolo-dental  .  .115 

Perissodactyle  ungulata,  teeth  of.  388 
Permanent  teeth,  eruption  of  .  206 
„  development  of  .  .146 

Persistent  dental  capsule  .  .  109 

Phacochaerus,  teeth  of  315,  331,  404 
Phalanger,  teeth  of  .  466,  472 

Phai-yngeal  teeth  of  carp  .  .  252 

,,  pike  .  .  244 

,,  pseudoscar  us  251 

,,  rachiodon  .  261 

,,  sc-arus .  .  249 

,,  wrasses  .  .  253 


Phascolarctos  .  .  *  . 

r  \ge 
328,  473 

Phascoiogale 

314,  467 

Phascolomys  . 

466,  479 

Phocidae,  teeth  of 

436,  438 

Pig,  teeth  of  . 

.  .  402 

Pigment  in  enamel 

58,  357 

Pike,  teeth  of  .  95,  129, 

216,  241 

Pinna,  structure  of  shell  . 

48,  161 

Plagiaulax,  teeth  of  .  289, 

466,  475 

Plagiostomi,  teeth  of 

.  .  239 

Platyrrhine  monkeys  . 

.  446 

Pleurodont,  meaning  of  term 

.  258 

Plicidentine  .  . 

.  82, 97 

Pliohippus  . 

.  393 

Poison  fang,  development  of 

.  166 

,,  mechanism  of 

.  .  266 

„  structure  of 

.  269 

,,  succession  of 

.  .  271 

Poison  gland 

.  273 

Polyprotodonts 

.  .  313 

Porcupine,  enamel  of  . 

.  51 

Poulton,  Mr.  . 

284,  289 

Precanine,  meaning  of  term 

.  .  9 

Premolars,  human 

.  15 

„  definition  of  . 

.  .  306 

Primates,  teeth  of 

.  442 

Priodon,  teeth  of 

.  .  335 

Pristis,  teeth  of  . 

.  237 

Proboscidea,  teeth  of 

.  .  377 

,,  affinities  with  rodents  386 

Procyonidae,  teeth  of 

.  .  434 

Proteles,  teeth  of 

.  429 

Protohippus  . 

.  .  393 

Pseudoscarus 

.  249 

Pteranodon 

.  .  278 

Pterodactyls,  teeth  of . 

.  277 

Pteromys,  enamel  of 

.  .  368 

Pteropus,  dentition  of  . 

.  358 

Pterosauria 

.  .  277 

Pulp,  the  .... 

.  100 

,,  degeneration  of 

.  .  104 

,,  nerves  of  . 

.  102 

,,  vessels  of 

.  .  ib. 

Python,  teeth  of 

221,  264 

R. 

Rachiodon,  teeth  of 

.  264 

Ramphorhynchus  . 

.  .  277 

Rat . 

.  144 

Rattlesnake,  teeth  of 

.  .  271 

Ray,  teeth  of 

.  238 

Rhinoceros,  teeth  of 

.  .  390 

Rhyncocephalus,  teeth  of  . 

.  260 

Rhytina,  teeth  of  . 

.  .  348 

Ridge  formulae  of  proboscidea 

.  385 

INDEX. 


491 


PAGE 

360,  367 
.  .  363 
50,  367 
.  .  37 
.  115 
.  .  238 


Rodentia,  teeth  of 

,,  milk  teeth  of  . 

„  enamel  of  . 

„  masseter  of 
Root  membrane  . 

Rostral  teeth  of  saw-fish  . 
Rudimentary  teeth,  examples  of 
282,  291,295,314, 

346,  382,  395,  412,  441 
,  milk  teeth,  examples 
of  .  328,  329,  377,  399 

Ruminants,  teeth  of  .  .  299 

„  absence  of  upper  in¬ 
cisors  in  .  .  *  295 


S. 


Salivary  glands  .  •  .39 

Salmon,  sexual  weapons  of  .  .  253 

Sarcophilus  .....  467 
Sargus,  enamel  of  .  .  .  .  60 

,,  teeth  of  .  .  .  .  253 

Saurians,  teeth  of  .  .  .  .  258 

Saw-fish,  teeth  of  237 

„  dentine  of  .  ...  87 

Scalpriform  incisors  of  rodents  .  361 
Scarus,  teeth  of  .  .  .  .  249 

Schreger,  lines  of  ...  66 

Sciuridae,  enamel  of  .  50, 368 


Sciurus,  enamel  fibres  of  .  .  368 

Seals,  teeth  of  .  .  331,  436 

Second  dentition  ....  208 
Secondary  dentine  .  .  .  .  98 

Selenodont,  meaning  of  term 

324,  405, 410 


Serres,  glands  of . 


.  115 


Sexual  weapons,  teeth  used  as  .  298 
differences  in  teeth  of 

apes  .  450 
in  teeth  of 
babirussa  407 
in  teeth  of 
boar  .  299 

in  teeth  of 
deer  299,  413 
in  teeth  of 
dugong 

299,  345 
in  teeth  of 
elephant  372 
in  teeth  of 
fish  .  253 

in  teeth  of 
horse  .  395 
in  teeth  of 
monkeys  299 


)> 


55 


59 


55 


55 


95 


59 


59 


55 


95 


59 


59 


5  5 


PAGE 

Sexual  differences  in  teeth  of 
narwal  .  .  .291, 299,  341 

Sharks,  development  of  teeth  of  .  122 
,,  teeth  of  .  .  231, 234 

Sharpey,  fibres  of  .  .  .108 

Sheep’s-head  fish,  teeth  of  .  .  253 
,,  „  ,,  enamel  of  .  60 

Shrews,  teeth  of  .  .  353,  357 

Simiadae . 446 

Sirenia,  teeth  of  .  .  .  345 

Sloths,  teeth  of  .  .  .  .  335 

Smilodon,  dentition  of  .  418,  432 

Snakes,  development  of  teeth  of  .  133 

,,  non -venomous  teeth  of  .  261 

,,  colubrine,  poisonous  266,  292 

,,  viperine,  poisonous  266,  292 

Socketed  teeth  ....  225 
Spermophilus,  enamel  of  .  .  368 

Sphenodon,  teeth  of  .  .  .  260 

Sphyraena,  teeth  of  ...  253 

Squalodon . 336 

Stegosaurus,  teeth  of  .  .  .  276 

Stellate  reticulum  of  enamel  organ 

139,  143,  166 
Stewart,  Prof.  .  .  .  260,  286 

Stratum  intermedium  of  enamel 

organ  .  .  139,  143 

,,  Malpighi,  the  .  115,  140 

Striae  of  enamel  prisms  .  .  54 

,,  of  Retzius  .  .  .  .  58 

Sturgeon . 252 

Sty  lino  dontidae  .  .  .  .  420 

Succession  of  teeth  in  armadillo  .  326 
,,  ,,  in  elephants  .  377 

,,  „  in  fish  .  .  253 

,,  ,,  in  lizards  .  258 

,,  ,,  in  mammals 

306,  327,  331 

,,  „  in  marsupials  466 

,,  ,,  in  osseous  fish  128 

,,  „  in  proboscidea  377 

,,  „  in  reptiles  .  130 

,,  ,,  in  sharks  .  .126 

„  ,,  in  snakes  .  133 

,,  ,,  in  poisonous 

snakes  .  271 

Supernumeraiy  teeth  in  dogs  .  427 
Sus  babirussa,  teeth  of  .  291,  407 

Sus  scrofa,  teeth  of  .  404 

Sword-fish  .  .  ...  241 


T. 

Talpa,  dentition  of  354 

Tamias,  enamel  of  .  .  .  .  368 


492 


INDEX. 


PAGE 


Tapir,  teeth  of  .  .  90,  389 

Tarsipes,  teeth  of  .  .  .  .  481 

Tatusia . 326 

Taxeopoda . 370 

Teeth,  equivalent  to  dermal  spines  2 
Teething  .  .  .  .  193, 204 

Teleostei,  teeth  of  .  .  .  .  241 

„  development  of  teeth  of  128 
Temporal  muscle,  action  of  .  .36 

Temporary  teeth,  eruption  of  .  .  202 


Tetralophodon 
Tetrodon,  teeth  of  . 
Theriodontia 
Thylacinus,  teeth  of 


Thylacoleo,  teeth  of 
Tiger,  teeth  of 
Tillodontia,  teeth  of 
Tillotherium,  teeth  of 
Tinoceras 
Tomes’  fibrils 

processes  of  ename 


.  322 
.  .  247 
.  277 
314,  328,  467, 
470 

.  475, 476 

.  423 
.  .  419 
.  418 
277,  419 
70,  73 
cells 


162 

164 

Tooth,  definition  of 

•  • 

1 

^  SRC  •  •  • 

•  • 

152 

„  germ. 

•  • 

121 

Tortoises,  teeth  of  . 

•  • 

258 

Toxodon,  teeth  of 

415 

Tragulina,  dentition  of  . 
Triacanthodon 

•  • 

411 

•  • 

468 

Trichechus,  teeth  of 

440 

Triconodon  . 

#  # 

466 

Triton  crist  atus 

•  • 

131 

Tusks  of  wild  boar 

•  • 

403 

„  of  elephant,  foreign 

bodies 

in 

•  • 

375 

Tylopoda 

•  • 

409 

Typical  tooth 

•  • 

315 

„  dentition 

.  304, 

482 

IT. 

PAGE 

Ungulata,  teeth  of  387 

„  molar  patterns  of  .  .  388 

Urotrichus . 319 

Ursus,  teeth  of  .  .  .  .  435 


Vampire,  teeth  of  .  .  357,  359 

Varanus,  teeth  of  259 

„  dentine  of  .  .  .  82 

Variability  of  teeth  .  .  296,  481 

Vaso-dentine  .  .  .88  et  seq . 

Viper,  teeth  of  ...  265 

„  succession  of  teeth  in  .  .271 

Viverridre,  teeth  of  427 

Vomer,  teeth  on  .  219,  243, 247 

W. 


Walrus,  teeth  of  .  .  .  .  440 

Wart-hog,  teeth  of  .315,  331,  404 
Whale,  rudimentary  teeth  of  337,  342 

Whalebone . 343 

Wisdom  teeth  .  .  .  21, 23 

„  of  lower  races  of 

man  .  .  .  458 

„  of  monkeys  447, 450, 

457 

Wolf-fish,  teeth  of  247 

Wombat,  teeth  of  .  .  .  .  479 

,,  enamel  of  .  .  .58 

Wrasse,  teeth  of  .  .  94,  253,  315 


Z. 

Zeuglodon . 336 

Ziphoid  cetacea,  teeth  of  .  .  338 


THE  END. 


BRADBURY,  AGNEW,  &  CO.,  PRINTERS,  WIIITEFRIARS. 


CATALOGUE  No.  7. 


DECEMBER,  1889. 


A  CATALOGUE 

OF 

Books  for  Students. 

INCLUDING  THE 


?  QUIZ-COMPENDS  ? 

CONTENTS. 


PAGE 

New  Series  of  Manuals,  2, 3, 4, 5 


Anatomy,  .  .  .  .  6 

Biology,  .  .  .  .11 

Chemistry,  .  .  .  .6 

Children’s  Diseases,  .  .  7 

Dentistry,  ....  8 
Dictionaries,  .  .  .8 

Eye  Diseases,  .  .  .8 

Electricity,  .  ...  9 

Gynaecology,  .  .  .10 

Hygiene,  ....  9 

Materia  Medica,  .  .  .9 

Medical  Jurisprudence,  .  9 

Miscellaneous,  .  .  10 


PAGE 

Obstetrics.  .  .  .  .10 

Pathology,  Histology, .  .  11 

Pharmacy,  .  .  .  .13 

Physical  Diagnosis,  .  .11 

Physiology,  .  .  .  .12 

Practice  of  Medicine,  .  .  12 

Prescription  Books,  .  .  12 

?  Quiz-Compends  ?  .  15,16 

Skin  Diseases,  .  .  .13 

Surgery,  .  .  .  .13 

Therapeutics,  .  .  .9 

Throat,  .  .  .  .14 


Urine  and  Urinary  Organs,  14 
Venereal  Diseases,  .  .  14 


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A  Manual  of  the  Practice  of  Surgery.  By  Wm.  J. 

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Surg.  in,  St.  Bartholomew’s  Hospital,  London,  etc. 

228  Illustrations. 

Presents  the  introductory  facts  in  Surgery  in  clear,  precise 
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BK.  H.  WALTER 


THE  NEW  SERIES  OF  MANUALS. 


3 


No.  2.  DISEASES  OF  WOMEN.  150  Illus. 

NEW  EDITION. 

The  Diseases  of  Women.  Including  Diseases  of  the 
Bladder  and  Urethra.  By  Dr.  F.  Winckel,  Professor 
of  Gynaecology  and  Director  of  the  Royal  University 
Clinic  for  Women,  in  Munich.  Second  Edition.  Re¬ 
vised  and  Edited  by  Theophilus  Parvin,  M.D., 
Professor  of  Obstetrics  and  Diseases  of  Women  and 
Children  in  Jefferson  Medical  College.  150  Engrav¬ 
ings,  most  of  which  are  original. 

"  The  book  will  be  a  valuable  one  to  physicians,  and  a  safe  and 
satisfactory  one  to  put  into  the  hands  of  students.  It  is  issued  in  a 
neat  and  attractive  form,  and  at  a  very  reasonable  price." — Boston 
Medical  and  Surgical  Journal. 


No.  3.  OBSTETRICS.  227  Illustrations. 

A  Manual  of  Midwifery.  By  Alfred  Lewis  Galabin, 
M.A.,  M.D.,  Obstetric  Physician  and  Lecturer  on  Mid¬ 
wifery  and  the  Diseases  of  Women  at  Guy’s  Hospital, 
London;  Examiner  in  Midwifery  to  the  Conjoint 
Examining  Board  of  England,  etc.  With  227  Illus. 

“  This  manual  is  one  we  can  strongly  recommend  to  all  who 
desire  to  study  the  science  as  well  as  the  practice  of  midwifery. 
Students  at  the  present  time  not  only  are  expected  to  know  the 
principles  of  diagnosis,  and  the  treatment  of  the  various  emergen¬ 
cies  and  complications  that  occur  in  the  practice  of  midwifery,  but 
find  that  the  tendency  is  for  examiners  to  ask  more  questions 
relating  to  the  science  of  the  subject  than  was  the  custom  a  few 
years  ago.  *  *  *  The  general  standard  of  the  manual  is  high ; 


_  _  _  ■ 

and  wherever  the  science  and  practice  of  midwifery  are  well  taughg^L 
it  will  be  regarded  as  one  of  the  most  important  text-books  on  the 
subject.” — London  Practitioner . 


0 


No.  4.  PHYSIOLOGY.  Fourth  Edition* 

321  ILLUSTRATIONS  AND  A  GLOSSARY. 

A  Manual  of  Physiology.  By  Gerald  F.  Yeo, 
f.r.c  s.,  Professor  of  Physiology  in  King’s  College, 
London.  321  Illustrations  and  a  Glossary  of  Terms. 
Fourth  American  from  second  English  Edition,  revised 
and  improved.  758  pages. 

This  volume  was  specially  prepared  to  furnish  students  with  a 
new  text-book  of  Physiology,  elementary  so  far  as  to  avoid  theories 
which  have  not  borne  the  test  of  time  and  such  details  of  methods 
as  are  unnecessary  for  students  in  our  medical  colleges. 

"The  brief  examination  I  have  given  it  was  so  favorable  that  I 
placed  it  in  the  list  of  text-books  recommended  in  the  circular  of  the 
University  Medical  College.’’ — Prof.  Lewis  A.  Stimson,  m.d., 
57  East  33d  Street,  New  York. 

Price  of  each  Book,  Cloth,  $3.00 ;  Leather,  $3.50. 


4 


THE  NEW  SERIES  OF  MANUALS. 


No.  5.  ORGANIC  CHEMISTRY. 

Or  the  Chemistry  of  the  Carbon  Compounds.  By  Prof. 
Victor  von  Richter,  University  of  Breslau.  Au¬ 
thorized  translation,  from  the  Fourth  German  Edition. 
By  Edgar  F.  Smith,  m.a.,  ph.d.  ;  Prof,  of  Chemistry 
in  University  of  Pennsylvania;  Member  of  the  Chem. 
Socs.  of  Berlin  and  Paris. 

“I  must  say  that  this  standard  treatise  is  here  presented  in  a 
remarkably  compendious  shape.” — J.  W.  Holland ,  m.d..  Professor 
of  Chemistry ,, Jefferson  Medical  College ,  Philadelphia. 

“  This  work  brings  the  whole  matter,  in  simple,  plain  language, 
to  the  student  in  a  clear,  comprehensive  manner.  The  whole 
method  of  the  work  is  one  that  is  more  readily  grasped  than  that  of 
older  and  more  famed  text-books,  and  we  look  forward  to  the  time 
when,  to  a  great  extent,  this  work  will  supersede  others,  on  the 
score  of  its  better  adaptation  to  the  wants  of  both  teacher  and 
student." — Pharmaceutical  Record. 

“Prof,  von  Richter’s  work  has  the  merit  of  being  singularly 
clear,  well  arranged,  and  for  its  bulk,  comprehensive.  Hence,  it 
will,  as  we  find  it  intimated  in  the  preface,  prove  useful  not  merely 
as  a  text-book,  but  as  a  manual  of  reference.” — The  Chemical 
News,  London. 

No.  6.  DISEASES  OF  CHILDREN. 

SECOND  EDITION. 

A  Manual.  By  J.  F.  Goodhart,  m.d.,  Phys.  to  the 
Evelina  Hospital  for  Children ;  Asst.  Phys.  to 
Guy’s  Hospital,  London.  Second  American  Edition. 
Edited  and  Rearranged  by  Louis  Starr,  m.d.,  Clinical 
Prof,  of  Dis.  of  Children  in  the  Hospital  of  the  Univ. 
of  Pennsylvania,  and  Physician  to  the  Children’s  Hos¬ 
pital,  Phila.  Containing  many  new  Prescriptions,  a  list 
of  over  50  Formulae,  conforming  to  the  U.  S.  Pharma¬ 
copoeia,  and  Directions  for  making  Artificial  Human 
Milk,  for  the  Artificial  Digestion  of  Milk,  etc.  Ulus. 

“  The  author  has  avoided  the  not  uncommon  error  of  writing  a 
book  on  general  medicine  and  labeling  it  ‘  Diseases  of  Children,’ 
but  has  steadily  kept  in  view  the  diseases  which  seemed  to  be 
incidental  to  childhood,  or  such  points  in  disease  as  appear  to  be  so 
peculiar  to  or  pronounced  in  children  as  to  justify  insistence  upon 
them.  *  *  *  A  safe  and  reliable  guide,  and  in  many  ways 
admirably  adapted  to  the  wants  of  the  student  and  practitioner.” — 
American  Journal  of  Medical  Science. 

Price  of  each  Book,  Cloth,  $3.00  :  Leather,  $3.50. 


THE  NEW  SERIES  OF  MANUALS. 


5 


No.  6.  Goodhart  and  Starr  : — Continued. 

“  Thoroughly  individual,  original  and  earnest,  the  work  evi¬ 
dently  of  a  close  observer  and  an  independent  thinker,  this  book, 
though  small,  as  a  handbook  or  compendium  is  by  no  means  made 
up  of  bare  outlines  or  standard  facts." — The  Therapeutic  Ga¬ 
zette. 

“  As  it  is  said  of  some  men,  so  it  might  be  said  of  some  books, 
that  they  are  *  born  to  greatness.'  This  new  volume  has,  we 
believe,  a  mission,  particularly  in  the  hands  of  the  younger 
members  of  the  profession.  In  these  days  of  prolixity  in  medical 
literature,  it  is  refreshing  to  meet  with  an  author  who  knows  both 
what  to  say  and  when  he  has  said  it.  The  work  of  Dr.  Goodhart 
(admirably  conformed,  by  Dr.  Starr,  to  meet  American  require¬ 
ments)  is  the  nearest  approach  to  clinical  teaching  without  the 
actual  presence  of  clinical  material  that  we  have  yet  seen." — New 
York  Medical  Record. 


No.  7.  PRACTICAL  THERAPEUTICS. 

FOURTH  EDITION,  WITH  AN  INDEX  OF  DISEASES. 

Practical  Therapeutics,  considered  with  reference  to 
Articles  of  the  Materia  Medica.  Containing,  also,  an 
Index  of  Diseases,  with  a  list  of  the  Medicines 
applicable  as  Remedies.  By  Edward  John  Waring, 
M.D.,  f.r.C.p.  Fourth  Edition.  Rewritten  and  Re¬ 
vised  by  Dudley  W.  Buxton,  m.d.,  Asst,  to  the  Prof, 
of  Medicine  at  University  College  Hospital. 

“  We  wish  a  copy  could  be  put  in  the  hands  of  every  Student  or 
Practitioner  in  the  country.  In  our  estimation,  it  is  the  best  book 
of  the  kind  ever  written." — N.  Y.  Medical  Journal. 

No.  8.  MEDICAL  JURISPRUDENCE  AND 
TOXICOLOGY. 

NEW,  REVISED  AND  ENLARGED  EDITION. 

By  John  J.  Reese,  m.d.,  Professor  of  Medical  Jurispru¬ 
dence  and  Toxicology  in  the  University  of  Pennsyl¬ 
vania  ;  President  of  the  Medical  Jurisprudence  Society 
of  Phila. ;  2d  Edition,  Revised  and  Enlarged. 

“  This  admirable  text-book.” — Amer.  Jour .  of  Med.  Sciences. 

“  We  lay  this  volume  aside,  after  a  careful  perusal  of  its  pages, 
with  the  profound  impression  that  it  should  be  in  the  hands  of  every 

doctor  and  lawyer.  It  fully  meets  the  wants  of  all  students . 

He  has  succeeded  in  admirably  condensing  into  a  handy  volume  all 
the  essential  points.” — Cincinnati  Lancet  and  Clinic. 

Price  of  each  Book,  Cloth,  $3,00;  Leather,  $3.50. 


6 


STUDENTS’  TEXT-BOOKS  AND  MANUALS. 


ANATOMY. 

Holden’s  Anatomy.  A  manual  of  Dissection  of  the  Human 
Body.  Fifth  Edition.  Enlarged,  with  Marginal  References  and 
over  200  Illustrations.  Octavo.  Cloth,  5.00;  Leather,  6.00 
Bound  in  Oilcloth,  for  the  Dissecting  Room,  $4.50. 

“No  student  of  Anatomy  can  take  up  this  book  without  being 
pleased  and  instructed.  Its  Diagrams  are  original,  striking  and 
suggestive,  giving  more  at  a  glance  than  pages  of  text  description. 
*  *  *  The  text  matches  the  illustrations  in  directness  of  prac¬ 
tical  application  and  clearness  of  detail.” — New  York  Medical 
Record. 

Holden’s  Human  Osteology.  Comprising  a  Description  of  the 
Bones,  with  Colored  Delineations  of  the  Attachments  of  the 
Muscles.  The  General  and  Microscopical  Structure  of  Bone  and 
its  Development.  With  Lithographic  Plates  and  Numerous  Illus¬ 
trations.  Seventh  Edition.  8vo.  Cloth,  6.00 

Holden’s  Landmarks,  Medical  and  Surgical.  4th  ed. 

Cloth,  1.25 

Heath’s  Practical  Anatomy.  Sixth  London  Edition.  24  Col¬ 
ored  Plates,  and  nearly  300  other  Illustrations.  Cloth,  5.00 

Potter’s  Compend  of  Anatomy.  Fourth  Edition.  117  Illus¬ 
trations.  Cloth,  1. 00;  Interleaved  for  Notes,  1.25 

CHEMISTRY. 

Bartley’s  Medical  Chemistry.  Second  Edition.  A  text-book 
prepared  specially  for  Medical,  Pharmaceutical  and  Dental  Stu¬ 
dents.  With  50  Illustrations,  Plate  of  Absorption  Spectra  and 
Glossary  of  Chemical  Terms.  Revised  and  Enlarged.  Cloth,  2.50 

***  This  book  has  been  written  especially  for  students  and  phy¬ 
sicians.  It  is  practical  and  concise,  dealing  only  with  those  parts 
of  chemistry  and  physics  pertaining  to  medicine ;  no  time  being 
wasted  in  long  descriptions  of  substances  and  theories  of  interest 
only  to  the  advanced  chemical  student. 

Bloxam’s  Chemistry,  Inorganic  and  Organic,  with  Experiments. 
Seventh  Edition.  Enlarged  and  Rewritten.  Nearly  300  Illus¬ 
trations.  Cloth,  4.50;  Leather,  5.50 

Richter’s  Inorganic  Chemistry.  A  text-book  for  Students. 
Third  American,  from  Fifth  German  Edition.  Translated  by 
Prof.  Edgar  F.  Smith,  ph.d.  89  Wood  Engravings  and  Colored 
Plate  of  Spectra.  Cloth,  2.00 

Richter’s  Organic  Chemistry,  or  Chemistry  of  the  Carbon 
Compounds.  Translated  by  Prof.  Edgar  F.  Smith,  ph.d. 
Illustrated.  Cloth,  3.00 ;  Leather,  3.50 

4®**  See  pages  2  to  j  /or  list  of  Students’  Manuals. 


STUDENTS’  TEXT-BOOKS  AND  MANUALS. 


7 


Chemistry  : — Continued. 

Trimble.  Practical  and  Analytical  Chemistry.  A  Course  in 
Chemical  Analysis,  by  Henry  Trimble,  Prof,  of  Analytical  Chem¬ 
istry  in  the  Phila.  College  of  Pharmacy.  Illustrated.  Third 
Edition.  8vo.  Cloth,  1.50 

Tidy.  Modern  Chemistry.  2d  Ed.  Cloth,  5.50 

Leffmann’s  Compend  of  Chemistry.  Inorganic  and  Organic. 
Including  Urinary  Analysis  and  the  Sanitary  Examination  of 
Water.  New  Edition.  Cloth,  1.00;  Interleaved  for  Notes,  1.25 

Muter.  Practical  and  Analytical  Chemistry.  Second  Edi¬ 
tion.  Revised  and  Illustrated.  Cloth,  2.00 

Holland.  The  Urine,  Common  Poisons,  and  Milk  Analysis, 
Chemical  and  Microscopical.  For  Laboratory  Use.  3d 

Edition,  Enlarged.  Illustrated.  Cloth,  1.00 

Van  Niiys.  Urine  Analysis.  Illus,  Cloth,  2.00 

Wolff’s  Applied  Medical  Chemistry.  By  Lawrence  Wolff, 
m.d.,  Demonstrator  of  Chemistry  in  Jefferson  Medical  College, 
Philadelphia.  Cloth,  1.00 

CHILDREN. 

Goodhart  and  Starr.  The  Diseases  of  Children.  A  Manual 
for  Students  and  Physicians.  By  J.  F.  Goodhart,  m.d.,  Physi¬ 
cian  to  the  Evelina  Hospital  for  Children ;  Assistant  Physician 
to  Guy’s  Hospital,  London.  American  Edition,  Revised  and 
Edited  by  Louis  Starr,  m.d..  Clinical  Professor  of  Diseases  of 
Children  in  the  Hospital  of  the  University  of  Pennsylvania; 
Physician  to  the  Children’s  Hospital,  Philadelphia.  Containing 
many  new  Prescriptions,  a  List  of  over  50  Formulae,  conforming 
to  the  U.  S.  Pharmacopoeia,  and  Directions  for  making  Arti¬ 
ficial  Human  Milk,  for  the  Artificial  Digestion  of  Milk,  etc. 
Second  Edition.  Illustrated.  Cloth,  3.00;  Leather,  3.50 

Day.  On  Children.  A  Practical  and  Systematic  Treatise. 
Second  Edition.  8vo.  752  pages.  Cloth,  3.00;  Leather,  4.00 

Meigs  and  Pepper.  The  Diseases  of  Children.  Seventh 
Edition.  8vo.  Cloth,  5.00;  Leather,  6.00 

Starr.  Diseases  of  the  Digestive  Organs  in  Infancy  and 
Childhood.  With  chapters  on  the  Investigation  of  Disease, 
and  on  the  General  Management  of  Children.  By  Louis  Starr, 
m.d.,  Clinical  Professor  of  Diseases  of  Children  in  the  Univer¬ 
sity  of  Pennsylvania;  with  a  section  on  Feeding,  including  special 
Diet  Lists,  etc.  Illus.  Cloth,  2.50 

4®°*  See  pages  15  and  id  for  list  of  ?  Quiz-  Compends  l 


8 


STUDENTS'  TEXT-BOOKS  AND  MANUALS. 


DENTISTRY. 

Fillebrown.  Operative  Dentistry.  330  Illustrations.  Just 
Ready.  Cloth,  2.50 

Flagg’s  Plastics  and  Plastic  Filling.  3d  Ed.  Preparing. 
Gorgas.  Dental  Medicine.  A  Manual  of  Materia  Medica  and 
Therapeutics.  Third  Edition.  Cloth,  3.50 

Harris.  Principles  and  Practice  of  Dentistry.  Including 
Anatomy,  Physiology,  Pathology,  Therapeutics,  Dental  Surgery 
and  Mechanism.  Twelfth  Edition.  Revised  and  enlarged  by 
Professor  Gorgas.  1028  Illustrations.  Cloth,  7.00  ;  Leather,  8.00 
Richardson’s  Mechanical  Dentistry.  Fifth  Edition.  569 
Illustrations.  8vo.  Cloth,  4.50;  Leather,  5.50 

Stocken’s  Dental  Materia  Medica.  Third  Edition.  Cloth,  2.50 
Taft’s  Operative  Dentistry.  Dental  Students  and  Practitioners. 

Fourth  Edition.  100  Illustrations.  Cloth,  4.25  ;  Leather,  5.00 
Talbot.  Irregularities  of  the  Teeth,  and  their  Treatment. 

Illustrated.  8vo.  Cloth,  2.00 

Tomes’  Dental  Anatomy.  Third  Ed.  191  Ulus.  Preparing. 
Tomes’  Dental  Surgery.  3d  Edition.  Revised.  292  Illus. 
772  Pages.  Cloth,  5.00 

DICTIONARIES. 

Cleaveland’s  Pocket  Medical  Lexicon.  Thirty-first  Edition. 
Giving  correct  Pronunciation  and  Definition  of  Terms  used  in 
Medicine  and  the  Collateral  Sciences.  Very  small  pocket  size. 

Cloth,  red  edges  .75  ;  pocket-book  style,  1.00 
Longley’s  Pocket  Dictionary.  The  Student’s  Medical  Lexicon, 
giving  Definition  and  Pronunciation  of  all  Terms  used  in  Medi¬ 
cine,  with  an  Appendix  giving  Poisons  and  Their  Antidotes, 
Abbreviations  used  in  Prescriptions,  Metric  Scale  of  Doses,  etc. 
24mo.  Cloth,  1. 00;  pocket-book  style,  1.25 

EYE. 

Arlt.  Diseases  of  the  Eye.  Including  those  of  the  Conjunc¬ 
tiva,  Cornea,  Sclerotic,  Iris  and  Ciliary  Body.  By  Prof.  Von 
Arlt.  Translated  by  Dr.  Lyman  Ware.  Ulus.  8vo.  Cloth,  2.50 
Hartridge  on  Refraction.  4th  Ed.  Cloth,  2.00 

Macnamara.  Diseases  of  the  Eye.  4th  Edition.  Revised. 

Colored  Plates  and  Wood  Cuts  and  Test  Types.  Cloth,  4.00 
Meyer.  Diseases  of  the  Eye.  A  complete  Manual  for  Stu¬ 
dents  and  Physicians.  270  Illustrations  and  two  Colored  Plates. 
8vo.  Cloth,  4.50;  Leather,  5.50 

Fox  and  Gould.  Compend  of  Diseases  of  the  Eye  and 
Refraction.  2d  Ed.  Enlarged.  71  Ulus.  39  Formulae. 

Cloth,  1. 00  ;  Interleaved  for  Notes,  1.25 
4®^  See pa^es  2  to  5  for  list  of  Students'  Manuals. 


STUDENTS’  TEXT-BOOKS  AND  MANUALS. 


9 


ELECTRICITY. 

Mason’s  Compend  of  Medical  and  Surgical  Electricity. 
With  numerous  Illustrations.  i2mo.  Cloth,  i.oo 

HYGIENE. 

Parkes’  (Ed.  A.)  Practical  Hygiene.  Seventh  Edition,  en¬ 
larged.  Illustrated.  8vo.  Cloth,  4.50 

Parkes’  (L.  C.)  Manual  of  Hygiene  and  Public  Health. 

12100.  Cloth,  2.50 

Wilson’s  Handbook  of  Hygiene  and  Sanitary  Science. 

Sixth  Edition.  Revised  and  Illustrated.  Cloth,  2.75 

MATERIA  MEDICA  AND  THERAPEUTICS. 

Potter’s  Compend  of  Materia  Medica,  Therapeutics  and 
Prescription  Writing.  Fifth  Edition,  revised  and  improved. 

Cloth,  1.00;  Interleaved  for  Notes,  1.25 
Biddle’s  Materia  Medica.  Eleventh  Edition.  By  the  late 
John  B.  Biddle,  m.  d..  Professor  of  Materia  Medica  in  Jefferson 
Medical  College,  Philadelphia.  Thoroughly  revised,  and  in  many 
parts  rewritten,  by  his  son,  Clement  Biddle,  m.d.,  Assistant 
Surgeon,  U.  S.  Navy,  assisted  by  Henry  Morris,  m.d.,  Demon¬ 
strator  of  Obstetrics  in  Jefferson  Medical  College.  8vo.,  illus¬ 
trated.  Cloth,  4.25;  Leather,  5.00 

Headland’s  Action  of  Medicines.  9th  Ed.  8vo.  Cloth,  3.00 
Potter.  Materia  Medica,  Pharmacy  and  Therapeutics. 
Including  Action  of  Medicines,  Special  Therapeutics,  Pharma¬ 
cology,  etc.  Second  Edition.  Cloth,  4.00;  Leather,  5.00 

Starr,  Walker  and  Powell.  Synopsis  of  Physiological 
Action  of  Medicines, based  upon  Prof.  H.  C.  Wood’s  “  Materia 
Medica  and  Therapeutics.”  3d  Ed.  Enlarged.  Cloth,  .75 
Waring.  Therapeutics.  With  an  Index  of  Diseases  and  an 
IndSx  of  Remedies.  A  Practical  Manual.  Fourth  Edition. 
Revised  and  Enlarged.  Cloth,  3.00;  Leather,  3.50 

MEDICAL  JURISPRUDENCE. 

Reese.  A  Text-book  of  Medical  Jurisprudence  and  Toxi¬ 
cology.  By  John  J.  Reese,  m.d..  Professor  of  Medical  Juris¬ 
prudence  and  Toxicology  in  the  Medical  Department  of  the 
University  of  Pennsylvania;  President  of  the  Medical  Juris¬ 
prudence  Society  of  Philadelphia;  Physician  to  St.  Joseph's 
Hospital;  Corresponding  Member  of  The  New  York  Medico¬ 
legal  Society.  2d  Edition.  Cloth,  3.00;  Leather,  3.50 

Woodman  and  Tidy’s  Medical  Jurisprudence  and  Toxi¬ 
cology.  C.hromo-Lithographic  Plates  and  116  Wood  engravings. 

Cloth,  7.50;  Leather,  8.50 
See  pages  ij  and  16  for  list  of  ?  Quiz-Compends  ? 


10  STUDENTS’  TEXT-BOOKS  AND  MANUALS. 


MISCELLANEOUS. 

Allingham.  Diseases  of  the  Rectum.  Fourth  Edition.  Illus¬ 
trated.  8vo.  Paper  covers,  .75;  Cloth,  1.25 

Beale.  Slight  Ailments.  Their  Nature  and  Treatment.  Illus¬ 
trated.  8vo.  Cloth,  1.25 

Domville  on  Nursing.  6th  Edition.  Cloth,  .75 

Gowers.  Diseases  of  the  Nervous  System.  341  Illus¬ 
trations.  Cloth,  6.50;  Leather,  7.50 

Mann’s  Manual  of  Psychological  Medicine,  and  Allied  Ner¬ 
vous  Diseases.  Their  Diagnosis,  Pathology  and  Treatment,  and 
their  Medico-Legal  Aspects.  Illus.  Cloth,  5.00;  Leather,  6.00 

Tanner.  Memoranda  of  Poisons.  Their  Antidotes  and  Tests. 
Sixth  Edition.  Revised  by  Henry  Leffmann,  m.d.  Cloth,  .75 

Parvin.  Lectures  on  Obstetric  Nursing.  32mo.  Cloth,  .75 

OBSTETRICS  AND  GYNAECOLOGY. 

Byford.  Diseases  of  Women.  The  Practice  of  Medicine  and 
Surgery,  as  applied  to  the  Diseases  and  Accidents  Incident  to 
Women.  By  W.  H.  Byford,  a.m.,  m.d.,  Professor  of  Gynaecology 
in  Rush  Medical  College  and  of  Obstetrics  in  the  Woman’s  Med¬ 
ical  College,  etc.,  and  Henry  T.  Byford,  m.d.,  Surgeon  to  the 
Woman’s  Hospital  of  Chicago  ;  Gynaecologist  to  St.  Luke’s 
Hospital,  etc.  Fourth  Edition.  Revised,  Rewritten  and  En¬ 
larged.  With  306  Illustrations,  over  100  of  which  are  original. 
Octavo.  832  pages.  Cloth,  5.00;  Leather,  6.00 

Cazeaux  and  Tarnier’s  Midwifery.  With  Appendix,  by 

Munde.  The  Theory  and  Practice  of  Obstetrics  ;  including  the 
Diseases  of  Pregnancy  and  Parturition,  Obstetrical  Operations, 
etc.  By  P.  Cazeaux.  Remodeled  and  rearranged,  with  revi¬ 
sions  and  additions,  by  S.  Tarnier,  m.d.,  Professor  of  Obstetrics 
and  Diseases  of  Women  and  Children  in  the  Faculty  of  Medicine 
of  Paris.  Eighth  American,  from  the  Eighth  French  and  First 
Italian  Edition.  Edited  by  Robert  J.  Hess,  m.d.,  Physician  to 
the  Northern  Dispensary,  Philadelphia,  with  an  appendix  by 
Paul  F.  Munde,  m.d..  Professor  of  Gynaecology  at  the  N.  Y. 
Polyclinic.  Illustrated  by  Chromo- Lithographs,  Lithographs, 
and  other  Full-page  Plates,  seven  of  which  are  beautifully  colored, 
and  numerous  Wood  Engravings.  Students’  Edition.  One 
Vol.,  8vo.  Cloth,  5.00;  Leather,  6.00 

Lewers’  Diseases  of  Women.  A  Practical  Text-Book.  139 
Illustrations.  Cloth,  2.25 

Parvin’s  Winckel’s  Diseases  of  Women.  Second  Edition. 

Including  a  Section  on  Diseases  of  the  Bladder  and  Urethra. 
Edited  by  Prof.  Theophilus  Parvin,  Jefferson  Medical  Col¬ 
lege,  Philadelphia.  150  Illustrations.  Second  Edition,  Revised 
and  Enlarged.  See  page  3.  Cloth,  3.00;  Leather,  3.50 

Morris.  Compend  of  Gynaecology.  Illustrated.  In  Press. 

See  pages  2  to  5  for  list  0/ New  Manuals. 


STUDENTS'  TEXT-BOOKS  AND  MANUALS. 


11 


Obstetrics  and  Gyncecology  : — Continued. 

Winckel’s  Obstetrics.  A  Text-book  on  Midwifery,  includ¬ 
ing  the  Diseases  of  Childbed.  By  Dr.  F.  Winckel,  Professor 
of  Gynaecology,  and  Director  of  the  Royal  University  Clinic  for 
Women,  in  Munich.  Authorized  Translation,  by  J.  Clifton 
Edgar,  m.d.,  Lecturer  on  Obstetrics,  University  Medical  Col¬ 
lege,  New  York,  with  nearly  200  handsome  illustrations,  the 
majority  of  which  are  original  with  this  work.  Octavo.  In  press. 
Landis’  Compend  of  Obstetrics.  Illustrated.  4th  edition, 
enlarged.  Cloth,  1.00;  Interleaved  for  Notes,  1.25 

Galabin’s  Midwifery.  A  New  Manual  for  Students.  By  A. 
Lewis  Galabin,  m.d.,  f.r.c.p.,  Obstetric  Physician  to  Guy's 
Hospital,  London,  and  Professor  of  Obstetrics  in  the  same  Insti¬ 
tution.  227  Illustrations.  See  page  3.  Cloth,  3.00;  Leather,  3.50 
Glisan’s  Modern  Midwifery.  2d  Edition.  Cloth,  3.00 

Rigby’s  Obstetric  Memoranda.  By  Alfred  Meadows,  m.d. 

4th  Edition.  Cloth,  .50 

Meadows’  Manual  of  Midwifery.  Including  the  Signs  and 
Symptoms  of  Pregnancy,  Obstetric  Operations,  Diseases  of  the 
Puerperal  State,  etc.  145  Illustrations.  494  pages.  Cloth,  2.00 
Swayne’s  Obstetric  Aphorisms.  For  the  use  of  Students 
commencing  Midwifery  Practice.  8th  Ed.  i2mo.  Cloth,  1.25 

PATHOLOGY.  HISTOLOGY.  BIOLOGY. 

Bowlby.  Surgical  Pathology  and  Morbid  Anatomy,  for 
Students.  135  Illustrations.  i2mo.  Cloth,  2.00 

Davis’  Elementary  Biology.  Illustrated.  Cloth,  4.00 

Rindfleisch’s  General  Pathology.  By  Prof.  Edward  Rind- 
fleisch.  Translated  by  Wm.  H.  Mercur,  m.d.  Edited  by  James 
Tyson,  m.d.,  Professor  of  Clinical  Medicine  in  the  University 
of  Pennsylvania.  i2mo.  Cloth,  2.00 

Gilliam’s  Essentials  of  Pathology.  A  Handbook  for  Students. 
47  Illustrations.  i2mo.  Cloth,  2.00 

***  The  object  of  this  book  is  to  unfold  to  the  beginner  the  funda¬ 
mentals  of  pathology  in  a  plain,  practical  way,  and  by  bringing 
them  within  easy  comprehension  to  increase  his  interest  in  the  study 
of  the  subject. 

Gibbes’  Practical  Histology  and  Pathology.  Third  Edition. 
Enlarged.  i2mo.  Cloth,  1.75 

Virchow’s  Post-Mortem  Examinations.  2d  Ed.  Cloth,  1.00 

PHYSICAL  DIAGNOSIS. 

Bruen’s  Physical  Diagnosis  of  the  Heart  and  Lungs.  By 

Dr.  Edward  T.  Bruen,  Assistant  Professor  of  Clinical  Medicine 
in  the  University  of  Pennsylvania.  Second  Edition,  revised. 
With  new  Illustrations.  i2mo.  Cloth,  1.50 

See  pages  15  and  ib  for  list  of  f  Quiz-Compends  ? 


12  STUDENTS'  TEXT-BOOKS  AND  MANUALS. 


PHYSIOLOGY. 

Yeo’s  Physiology.  Fourth  Edition.  The  most  Popular  Stu¬ 
dents’  Book.  By  Gerald  F.  Yeo,  m.d.,  f.r.c.s..  Professor  of 
Physiology  in  King's  College,  London.  Small  Octavo.  758 
pages.  321  carefully  printed  Illustrations.  With  a  Full 
Glossary  and  Index.  See  Page  3.  Cloth,  3.00;  Leather,  3.50 

Brubaker’s  Compend  of  Physiology.  Illustrated.  Fifth 
Edition.  Cloth,  1.00;  Interleaved  for  Notes,  1.25 

Stirling.  Practical  Physiology,  including  Chemical  and  Ex¬ 
perimental  Physiology.  142  Illustrations.  Cloth,  2.25 

Kirke’s  Physiology.  New  12th  Ed.  Thoroughly  Revised  and 
Enlarged.  502  Illustrations.  Cloth,  4.00;  Leather,  5.00 

Landois’  Human  Physiology.  Including  Histology  and  Micro¬ 
scopical  Anatomy,  and  with  special  reference  to  Practical  Medi¬ 
cine.  Third  Edition.  Translated  and  Edited  by  Prof.  Stirling. 
692  Illustrations.  Cloth,  6.50;  Leather,  7.50 

“  With  this  Text-book  at  his  command,  no  student  could  fail  in 
his  examination.” — Lancet. 

Sanderson’s  Physiological  Laboratory.  Being  Practical  Ex¬ 
ercises  for  the  Student.  350  Illustrations.  8vo.  Cloth,  5.00 

Tyson’s  Cell  Doctrine.  Its  History  and  Present  State.  Illus¬ 
trated.  Second  Edition.  Cloth,  2.00 

PRACTICE. 

Roberts’  Practice.  New  Revised  Edition.  A  Handbook 
of  the  Theory  and  Practice  of  Medicine.  By  Frederick  T. 
Roberts,  m.d.  ;  m.r.c.p.,  Professor  of  Clinical  Medicine  and 
Therapeutics  in  University  College  Hospital,  London.  Seventh 
Edition.  Octavo.  Cloth,  5.50  ;  Sheep,  6.50 

Hughes.  Compend  of  the  Practice  of  Medicine.  3d  Ed- 
Two  parts,  each,  Cloth,  1.00;  Interleaved  for  Notes,  1.25 

Part  i. — Continued,  Eruptive  and  Periodical  Fevers,  Diseases 
of  the  Stomach,  Intestines,  Peritoneum,  Biliary  Passages,  Liver, 
Kidneys,  etc.,  and  General  Diseases,  etc. 

Part  ii. — Diseases  of  the  Respiratory  System,  Circulatory 
System  and  Nervous  System;  Diseases  of  the  Blood,  etc. 

Physician’s  Edition.  Including  a  Section  on  Skin  Diseases. 
With  Index.  1  Vol.  Full  Morocco,  Gilt,  2.50 

Tanner’s  Index  of  Diseases,  and  Their  Treatment.  Cloth,  3.00 
“  This  work  has  won  for  itself  a  reputation.  ...  It  is,  in 
truth,  what  its  Title  indicates.” — N.  Y.  Medical  Record. 

PRESCRIPTION  BOOKS. 

Wythe’s  Dose  and  Symptom  Book.  Containing  the  Doses 
and  Uses  of  all  the  principal  Articles  of  the  Materia  Medica,  etc. 
Seventeenth  Edition.  Completely  Revised  and  Rewritten.  Just 
Ready.  32mo.  Cloth,  1.00;  Pocket-book  style,  1.25 

Pereira’s  Physician’s  Prescription  Book.  Containing  Lists 
of  Terms,  Phrases,  Contractions  and  Abbreviations  used  in 
Prescriptions  Explanatory  Notes,  Grammatical  Construction  of 
Prescriptions,  etc.,  etc.  By  Professor  Jonathan  Pereira,  m.d. 
Sixteenth  Edition.  32010.  Cloth,  1. 00;  Pocket-book  style,  1.25 

4®“  See  pages  2  to  5  for  list  of  New  Manuals. 


STUDENTS'  TEXT-BOOKS  AND  MANUALS.  13 


PHARMACY. 

Stewart’s  Compend  of  Pharmacy.  Based  upon  Remington’s 
Text-Book  of  Pharmacy.  Second  Edition,  Revised. 

Cloth,  i.oo  ;  Interleaved  for  Notes,  1.25 

SKIN  DISEASES. 

Anderson,  (McCall)  Skin  Diseases.  A  complete  Text-Book, 
with  Colored  Plates  and  numerous  Wood  Engravings.  8vo. 
Just  Ready.  Cloth,  4.50  ;  Leather,  5.50 

“  We  welcome  Dr.  Anderson’s  work  not  only  as  a  friend,  but  as 
a  benefactor  to  the  profession,  because  the  author  has  stricken  off 
mediaeval  shackles  of  insuperable  nomenclature  and  made  crooked 
ways  straight  in  the  diagnosis  and  treatment  of  this  hitherto  but 
little  understood  class  of  diseases.  The  chapter  on  Eczema  is 
alone  worth  the  price  of  the  book.” — Nashville  Medical  News. 

“  Worthy  its  distinguished  author  in  every  respect;  a  work  whose 
practical  value  commends  it  not  only  to  the  practitioner  and  stu¬ 
dent  of  medicine,  but  also  to  the  dermatologist.” — Janies  Nevetts 
Hyde ,  m.d.,  Prof,  of  Skin  and  Venereal  Diseases,  Rush  Medical 
College,  Chicago. 

Van  Harlingen  on  Skin  Diseases.  A  Handbook  of  the  Dis¬ 
eases  of  the  Skin,  their  Diagnosis  and  Treatment  (arranged  alpha¬ 
betically).  By  Arthur  Van  Harlingen,  m.d.,  Clinical  Lecturer 
on  Dermatology,  Jefferson  Medical  College;  Prof,  of  Diseases  of 
the  Skin  in  the  Philadelphia  Polyclinic.  2d  Edition.  Enlarged. 
With  colored  and  other  plates  and  illustrations.  i2mo.  Cloth,  2.50 

Bulkley.  The  Skin  in  Health  and  Disease.  By  L.  Duncan 
Bulkley,  Physician  to  the  N.  Y.  Hospital.  Illus.  Cloth,  .50 

SURGERY. 

Jacobson.  Operations  in  Surgery.  A  Systematic  Handbook 
for  Physicians,  Students  and  Hospital  Surgeons.  By  W.  H.  A. 
Jacobson,  b.a.,  Oxon.  f.r.c.s.  Eng.;  Ass’t  Surgeon  Guy’s  Hos¬ 
pital  ;  Surgeon  at  Royal  Hospital  for  Children  and  Women,  etc. 
With  199  finely  printed  illustrations.  1006  pages.  8vo. 

Cloth.  $5.00;  Leather,  $6.00 
Heath’s  Minor  Surgery,  and  Bandaging.  Ninth  Edition.  142 
Illustrations.  60  Formulae  and  Diet  Lists.  Cloth,  2.00 

Horwitz’s  Compend  of  Surgery,  including  Minor  Surgery, 
Amputations,  Fractures,  Dislocations,  Surgical  Diseases,  and  the 
Latest  Antiseptic  Rules,  etc.,  with  Differential  Diagnosis  and 
Treatment.  By  Orville  Horwitz,  b.s.,  m.d..  Demonstrator  of 
Surgery,  Jefferson  Medical  College  ;  Chief,  Out-Patient  Surgi¬ 
cal  Department,  Jefferson  Medical  College  Hospital.  3d  edition. 
Very  much  Enlarged  and  Rearranged.  91  Illustrations  and 
77  Formulae.  i2mo.  No.  q  ?  Quiz-  Comp  end  ?  Series. 

Cloth,  1.00;  Interleaved  for  the  addition  of  Notes,  1.25. 

Pye’s  Surgical  Handicraft.  A  Manual  of  Surgical  Manipula¬ 
tions,  Minor  Surgery,  Bandaging,  Dressing,  etc.,  etc.  With 
special  chapters  on  Aural  Surgery,  Extraction  of  Teeth,  Anaes¬ 
thetics,  etc.  208  Illustrations.  8vo.  Cloth,  5.00 

Swain’s  Surgical  Emergencies.  New  Edition.  Illus.  Clo.,1.50 

See  pages  15  and  lb  for  list  of  ?  Quiz-  Contends  f 


14  STUDENTS'  TEXT-BOOKS  AND  MANUALS. 


Surgery  : — Continued. 

Walsham.  Manual  of  Practical  Surgery.  For  Students  and 
Physicians.  By  Wm.  J.  Walsham,  m.d. ,  f.r.c.s.,  Asst.  Surg. 
to,  and  Dem.  of  Practical  Surg.  in,  St.  Bartholomew’s  Hospital, 
Surgeon  to  Metropolitan  Free  Hospital,  London.  With  236 
Engravings.  See  Page  2.  Cloth,  3.00;  Leather,  3.50 

THROAT. 

Mackenzie.  Diseases  of  the  (Esophagus,  Nose  and  Naso¬ 
pharynx.  By  Sir  Morell  Mackenzie,  m.d.,  Senior  Physician  to 
the  Hospital  for  Diseases  of  the  Chest  and  Throat;  Lecturer 
on  Diseases  of  the  Throat  at  the  London  Hospital,  etc.,  with 
Formulae  and  93  Illustrations.  Being  Vol.  11,  complete  in  itself, 
of  Dr.  Mackenzie’s  text-book  on  the  Throat  and  Nose. 

Cloth,  3.00;  Leather,  4.00 

“  It  is  both  practical  and  learned ;  abundantly  and  well  illustrated ; 

its  descriptions  of  disease  are  graphic  and  the  diagnosis  the  best  we 

have  anywhere  seen.” — Philadelphia  Medical  Times. 

Cohen.  The  Throat  and  Voice.  Illustrated.  Cloth,  .50 

James.  Sore  Throat.  Its  Nature,  Varieties  and  Treatment. 
i2mo.  Illustrated.  Paper  cover,  .75 ;  Cloth,  1.25 

URINE,  URINARY  ORGANS,  ETC. 

Acton.  The  Reproductive  Organs.  In  Childhood,  Youth, 
Adult  Life  and  Old  Age.  Seventh  Edition.  Cloth,  2.00 

Beale.  Urinary  and  Renal  Diseases  and  Calculous  Disorders. 
Hints  on  Diagnosis  and  Treatment.  i2mo.  Cloth,  1.75 

Holland.  The  Urine,  and  Common  Poisons  and  The 
Milk.  Chemical  and  Microscopical,  for  Laboratory  Use.  Illus¬ 
trated.  Third  Edition,  umo.  Interleaved.  Cloth,  1.00 

Ralfe.  Kidney  Diseases  and  Urinary  Derangements.  42  Illus¬ 
trations.  i2mo.  572  pages.  Cloth,  2.75 

Legg.  On  the  Urine.  A  Practical  Guide.  6th  Ed.  Cloth,  .75 

Marshall  and  Smith.  On  the  Urine.  The  Chemical  Analysis  of 
the  Urine.  By  John  Marshall,  m.d.,  Chemical  Laboratory,  Univ. 
of  Penna;  and  Prof.  E.  F.  Smith,  ph.d.  Col.  Plates.  Cloth,  1.00 

Thompson.  Diseases  of  the  Urinary  Organs.  Eighth 
London  Edition.  Illustrated.  Cloth,  3.50 

Tyson.  On  the  Urine.  A  Practical  Guide  to  the  Examination 
of  Urine.  With  Colored  Plates  and  Wood  Engravings.  6th  Ed. 
Enlarged.  i2mo.  Cloth,  1.50 

-  Bright’s  Disease  and  Diabetes.  Illus.  Cloth,  3.50 

Van  Niiys,  Urine  Analysis.  Illus.  Cloth,  2.00 

VENEREAL  DISEASES. 

Hill  and  Cooper.  Student’s  Manual  of  Venereal  Diseases, 
with  Formulae.  Fourth  Edition.  i2mo.  Cloth,  1.00 

Durkee.  On  Gonorrhoea  and  Syphilis.  Illus.  Cloth,  3.50 

JSSr  See  pages  ij  and  ib  for  list  of  ?  Quiz-Compends  ? 


NEW  AND  REVISED  EDITIONS. 


?QUIZ-COMPENDS? 


The  Best  Compends  for  Students’  Use 
in  the  Quiz  Class,  and  when  Pre¬ 
paring  for  Examinations. 


Compiled  in  accordance  with,  the  latest  teachings  of  promi¬ 
nent  lecturers  and  the  most  popular  Text-books. 

They  form  a  most  complete,  practical  and  exhaustive 
set  of  manuals,  containing  information  nowhere  else  col¬ 
lected  in  such  a  condensed,  practical  shape.  Thoroughly 
up  to  the  times  in  every  respect,  containing  many  new 
prescriptions  and  formulae,  and  over  two  hundred  and 
thirty  illustrations,  many  of  which  have  been  drawn  and 
engraved  specially  for  this  series.  The  authors  have  had 
large  experience  as  quiz-masters  and  attaches  of  colleges, 
with  exceptional  opportunities  for  noting  the  most  recent 
advances  and  methods.  The  arrangement  of  the  subjects, 
illustrations,  types,  etc.,  are  all  of  the  most  approved 
form,  and  the  size  of  the  books  is  such  that  they  may  be 
easily  carried  in  the  pocket.  They  are  constantly  being 
revised,  so  as  to  include  the  latest  and  best  teachings,  and 
can  be  used  by  students  of  any  College  of  medicine,  den¬ 
tistry  or  pharmacy. 

Cloth,  each  $1.00.  Interleaved  for  Notes,  $1.25. 

No.  1.  HUMAN  ANATOMY,  “  Based  upon  Gray.”  Fourth 
Edition,  including  Visceral  Anatomy,  formerly  published 
separately.  Over  100  Illustrations.  By  Samuel  O.  L. 
Potter,  m.a.,  m.d.,  late  A.  A.  Surgeon  U.  S.  Army.  Professor 
of  Practice,  Cooper  Medical  College,  San  Francisco. 

Nos.  2  and  3.  PRACTICE  OF  MEDICINE.  Third  Edition.  ' 

By  Daniel  E.  Hughes,  m.d.,  Demonstrator  of  Clinical  Medi-  « 

cine  in  Jefferson  Medical  College,  Philadelphia.  In  two  parts. 

Part  I. — Continued,  Eruptive  and  Periodical  Fevers,  Diseases 
of  the  Stomach,  Intestines,  Peritoneum,  Biliary  Passages,  Liver, 
Kidneys,  etc.  (including  Tests  for  Urine),  General  Diseases,  etc. 

Part  II. — Diseases  of  the  Respiratory  System  (including  Phy¬ 
sical  Diagnosis),  Circulatory  System  and  Nervous  System;  Dis¬ 
eases  of  the  Blood,  etc. 

***  These  little  books  can  be  regarded  as  a  full  set  of  notes  upon 
the  Practice  of  Medicine,  containing  the  Synonyms,  Definitions, 
Causes,  Symptoms,  Prognosis,  Diagnosis,  Treatment,  etc.,  of  each 
disease,  and  including  a  number  of  prescriptions  hitherto  unpub¬ 
lished. 

(over.) 


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BLAKISTON’S  ?  QUIZ-COMPENDS  ? 

Continued. 

Bound  in  Cloth,  $1.00.  Interleaved,  for  Notes,  $1.25 

No.  4.  PHYSIOLOGY,  including  Embryology.  Fifth 
Edition.  By  Albert  P.  Brubaker,  m.d.,  Prof,  of  Physiology, 
Penn’a  College  of  Dental  Surgery  ;  Demonstrator  of  Physiology 
in  Jefferson  Medical  College,  Philadelphia.  Revised,  Enlarged 
and  Illustrated. 

No.  5.  OBSTETRICS.  Illustrated.  Fourth  Edition.  By 

Henry  G.  Landis,  m.d.,  Prof,  of  Obstetrics  and  Diseases  of 
Women,  in  Starling  Medical  College,  Columbus,  O.  Revised 
Edition.  New  Illustrations. 

No.  6.  MATERIA  MEDICA,  THERAPEUTICS  AND 
PRESCRIPTION  WRITING.  Fifth  Revised  Edition. 

With  especial  Reference  to  the  Physiological  Action  of  Drugs, 
and  a  complete  article  on  Prescription  Writing.  Based  on  the 
Last  Revision  of  the  U.  S.  Pharmacopoeia,  and  including  many 
unofficinal  remedies.  By  Samuel  O.  L.  Potter,  m.a.,  m.d., 
late  A.  A.  Surg.  U.  S.  Army;  Prof,  of  Practice,  Cooper  Medical 
College,  San  Francisco.  Improved  and  Enlarged,  with  Index. 

No.  7.  GYNAECOLOGY.  A  Compend  of  Diseases  of  Women. 
By  Henry  Morris,  m.d..  Demonstrator  of  Obstetrics,  Jefferson 
Medical  College,  Philadelphia. 

No.  8.  DISEASES  OF  THE  EYE  AND  REFRACTION, 

including  Treatment  and  Surgery.  By  L.  Webster  Fox,  m.d., 
Chief  Clinical  Assistant  Ophthalmological  Dept.,  Jefferson  Med¬ 
ical  College,  etc.,  and  Geo.  M.  Gould,  m.d.  71  Illustrations,  39 
Formulae.  Second  Enlarged  and  improved  Edition.  Index. 

No.  9.  SURGERY.  Illustrated.  Third  Edition.  Including 
Fractures,  Wounds,  Dislocations,  Sprains,  Amputations  and 
other  operations;  Inflammation,  Suppuration,  Ulcers,  Syphilis, 
Tumors,  Shock,  etc.  Diseases  of  the  Spine,  Ear,  Bladder,  Tes¬ 
ticles,  Anus,  and  other  Surgical  Diseases.  By  Orville  Horwitz, 
a.m.,  m.d.,  Demonstrator  of  Surgery,  Jefferson  Medical  Col¬ 
lege.  Revised  and  Enlarged.  77  Formulae  and  91  Illustrations. 

No.  10.  CHEMISTRY.  Inorganic  and  Organic.  For  Medical 
and  Dental  Students.  Including  Urinary  Analysis  and  Medical 
Chemistry.  By  Henry  Lf.ffmann,  m.d..  Prof,  of  Chemistry  in 
Penn’a  College  of  Dental  Surgery,  Phila.  A  new  Edition,  Revised 
and  Rewritten,  with  Index. 

No.  11.  PHARMACY.  Based  upon  “  Remington’s  Text-book 
of  Pharmacy.”  By  F.  E.  Stewart,  m.d.,  ph.g.,  Quiz-Master 
at  Philadelphia  College  of  Pharmacy.  Second  Edition,  Revised. 

Bound  in  Cloth,  $1.  Interleaved,  for  the  Addition  of  Notes,  $1.25. 

These  books  are  constantly  revised  to  keep  up  with 
the  latest  teachings  and  discoveries ,  so  that  they  contain 
all  the  new  methods  and  principles.  No  series  of  books 
are  so  complete  in  detail ,  concise  in  language ,  or  so  well 
printed  and  bound.  Each  one  forms  a  complete  set  of 
notes  upon  the  subject  tinder  consideration. 

Descriptive  Circular  Free. 


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